UNIVERSITY  OF  CALIFORNIA, 

DEPARTMENT  OF  CIVIL  ENGINEERING 

BERKELEY,  CALIFORNIA 


A  STUDY  OF;T;HE:; ; 

HEARTH 


A    TREATISE    ON    THE    OPEN    HEARTH    FURNACE 

AND    THE    MANUFACTURE    OF 

OPEN  HEARTH  STEEL 


BY 

HARBISON-WALKER    REFRACTORIES    CO. 

PITTSBURGH 

1909 


Copyright,  igog,  by 
Harbison-Walker  Refractories  Co. 


CONTENTS 

CHAPTER   I 

PAGE 

STEEL,    DEFINITION 9 

Processes  of  Manufacture 12 

DESCRIPTION   OF   OPEN   HEARTH   FURNACE          .         .  14 

DETAILS   OF   FURNACE 16 

ROOF .  16 

Hearth  and  Bottom 18 

Material  for  Bottoms    .         .         .         .         .         .  19 

Acid  Materials 20 

Neutral  Materials 21 

Basic  Materials 23 

Construction  of  Acid  Bottom         .         .         .         .  25 

Tap  Hole 25 

Bottom      .         . 26 

Wash  Heat 26 

Construction  of  Basic  Bottom      .         .         .         .  27 

Tap  Hole 27 

Bottom 27 

Wash  Heat 29 

Front  and  Back  Walls 29 

Bulkheads 30 

Ports 31 

Regenerators 34 

Slag  Pockets 38 

Uptakes  or  Vertical  Flues   .....  39 

Horizontal  Flues 39 

Gas  and  Air  Valves      ......  39 

Dampers 40 

Stacks 41 

Special  Furnaces    .......  41 

CHAPTER   II 

FUELS 43 

Natural  Gas 43 

Artificial  Gas          .......  44 

Fuel  for  making  Producer  Gas  ....  47 

Oil 48 

785297 


CONTENTS—  Continued 

CHAPTER    III  PAGE 

ACID   OPEN   HEARTH   PROCESS      .....  50 

Charge 50 

Proportioning  the  Charge 51 

Method  of  Charging 55 

Elimination  of  Impurities 56 

Melting    .         . 56 

Elimination  during  Melting          .        .        .  57 

Elimination  after  Melting     .        .         .        .  58 

Slag 62 

CHAPTER    IV 

RECARBURIZATION 65 

Recarburizers           ......  66 

Methods  of  Additions     .....  66 

Tapping 71 

Sulphur 72 

Samples  and  Tests 73 

CHAPTER   V 

BASIC   OPEN   HEARTH   PROCESS 75 

Method 75 

Phosphorous 76 

Sulphur 76 

Lime  Addition        .......  76 

Ore  Additions 78 

Charge 78 

Method  of  Charging 80 

Elimination  of  Phosphorous        ....  80 

Elimination  of  Sulphur 83 

Slag 84 

Removal  of  Slag 87 

Recarburization      .        .         .         .        .        .        .  87 

CHAPTER    VI 

SPECIAL  PROCESSES 89 

Talbot  Process 89 

Monell  Process       .......  90 

Bertrand-Thiel  Process 90 

Duplex  Process 91 


PREFACE 

REALIZING  as  we  do  that  only  by 
a  full  understanding  of  all  the 
conditions  encountered  in  actual 
Open  Hearth  practice,  can  refrac- 
tory materials  be  so  manufac- 
tured as  to  maintain  the  highest 
standard  for  such  work,  we  have  made  this 
study  of  Open  Hearth  steel  furnaces  and  their 
operation  essentially  for  the  use  of  our  Opera- 
ting Department. 

So  much  interest  in  this  article,  however, 
has  been  shown  by  a  number  of  Open  Hearth 
superintendents,  who  have  suggested  it  as 
being  of  interest  to  iron  and  steel  men 
generally,  that  we  have  decided  to  publish  it 
in  this  form. 

This  study  claims  no  originality.  Its  aim  is 
to  put  into  as  concise  form  as  may  be,  the  prin- 
ciples involved,  together  with  such  detailed 
description  as  may  render  the  subject  matter 
plain  to  one  familiar  with  no  more  than  the 
most  elementary  principles  of  chemistry  and 
metallurgy.  Other  articles  will  be  issued  from 
time  to  time  on  blast  furnaces  and  hot  blast 
stoves,  heating  and  puddling  furnaces,  etc., 
any  or  all  of  which  may  be  obtained  by  a 
request  to  be  put  on  our  mailing  list. 


A  STUDY  OF  THE  OPEN  HEARTH 

CHAPTER  :I/  '• 

STEEL:      /;,  :    \  '.'  \'j  \  •/ ;,  *>\  ': . 

Definition:  In  possibly  no  other  industry 
has  there  been  so  much  disputation,  and  to  so 
little  avail,  as  in  the  steel  industry  over  a  correct 
and  all  -  comprehensive  definition  of  steel  as 
distinguished  from  wrought  iron.  Committees, 
national  and  international,  have  been  appointed 
and  their  recommendations  made,  but  changes  in 
processes  of  manufacture  and  in  current  commer- 
cial usage  have  made  these  recommendations 
void  of  practical  value. 

Previous  to  modern  methods  of  steel  manufac- 
ture, such  as  the  Bessemer  and  the  Open  Hearth, 
hardening  or  tempering  in  water  indicated  steel ; 
failure  to  harden,  wrought  iron.  However,  with 
the  advent  of  these  processes,  a  large  part  of  their 
output,  universally  recognized  as  steel,  fails  to 
come  within  the  terms  of  such  description. 

It  is  seemingly  impossible  to  formulate  a 
definition  that  will  exactly  fit  every  case,  but  in 
general  that  given  by  Campbell,  as  being  that 
in  common  commercial  usage,  although  but  a 
definition  by  process  rather  than  characteristics, 
seems  best,  namely: 

(1)  Wrought  iron  is  the  product  of  the  puddle 
furnace. 

(2)  Steel  is  the   product  of  the   cementation 
process  or  the  malleable  compounds  of  iron  made 
in  the  crucible,  converter  or  open  hearth. 


MODERN  OPEN  HEARTH  FURNACE 

HARBiSGN-WALKER   REFRACTORIES  CO. 
PITTSBURG  PA. 

AUG.  20,    1909. 


SECTION  THROUGH  PORTS  AND  REGENERATIVE  CHAMBER 
10 


A        STUDY        OF        THE         OPEN         HEARTH 
PROCESSES    OF    MANUFACTURE 

There  are  practically  but  three  processes  of 
steel  making: 

(1)  Crucible,   invented  in  Sheffield,  England, 
by  Huntsman  in  1740. 

(2)  Bessemer,  invented   by   Henry  Bessemer 
in  1855.     Priority  over  Bessemer  in  the  invention 
of  this  process  is  claimed  by  an  American,  Kelly, 
although  his  American  patent  was  applied  for  in 
1857,   about   a   year   after   Bessemer 's   American 
patent  was    allowed    and    two    years    after    his 
English  patent.     Kelly's  application  was  granted 
on  grounds  of  priority,  but  considerable  litigation 
ensued,  a  compromise  finally  being  effected. 

(3)  Open    Hearth,    by  Charles,    William    and 
Frederick  Siemens  in  1861. 

The  crucible  process,  because  of  its  necessarily 
high  cost,  is  restricted  to  high  grade  steel  for 
cutlery,  tools,  intricate  parts  of  machinery,  etc. 

The  Bessemer  process,  quantitatively  until 
the  year  1908  the  leading  process  of  steel  manu- 
facture, is  unquestionably  giving  way  to  the 
Open  Hearth,  and  there  is  comparatively  small 
chance  that  we  shall  in  the  future  see  any  new 
Bessemer  plants  of  importance. 

This  is  due  primarily  to  the  growing  scarcity 
of  ores  from  which  can  be  made  pig  either  suffi- 
ciently low  in  phosphorus  for  the  acid  Bessemer 
or  sufficiently  high  for  basic  Bessemer.  In  the 
acid  process  none  of  the  phosphorous  being  re- 
moved, we  are  limited  to  such  pig  as  contains 
only  an  amount  of  phosphorous  allowable  in  the 


A    STUDY    OF    THE    OPEN    HEARTH 

finished  steel.  On  the  other  hand,  in  the  basic 
Bessmer,  this  element  must  be  sufficiently  high, 
say  2^  to  3  per  cent.,  to  supply  with  the  man- 
ganese and  carbon  fuel  to  oxidize  and  keep  hot 
the  charge,  otherwise  a  "cold  heat"  will  result. 
The  Open  Hearth  now  manufactures  more 
steel  than  any  other  process,  and  is  undoubtedly 
destined  to  make  still  greater  strides,  its  relative 
tonnage  as  compared  with  Bessemer  is  here 
indicated: 

a  s     j    6,609,017  .  .  .  Bessemer 

I    2,230,292  .  .  .  Open  Hearth 

Tft^o      J    7,586,354  .  .  .  Bessemer 

j    2,947,316  .  .  .  Open  Hearth 

j    6,684,770  .  .  .  Bessemer 

1    3,398,135  •  •  •  Open  Hearth 

TOOT      J    8,713,302  .  .  .  Bessemer 

"j    4,656,309  .  .  .  Open  Hearth 

Too2      J    9>!38,363  •  •  •  Bessemer 

\    5,687,729  .  .  .  Open  Hearth 

mo-?      f    8,592,829  .  .  .  Bessemer 

1903     }    5,829,911  .  .  .  Open  Hearth 

j    7,859,140  •  •  •  Bessemer 

(    5,908,166  .  .  .  Open  Hearth 

j  10,914,372  .  .  .  Bessemer 

{   8,971,376  .  .  Open  Hearth 

,      j  12,275,830  .  .  .  Bessemer 

\  10,980,413  .  .  .  Open  Hearth 

j  11,667,549  •  •  •  Bessemer 

97      "(11,549,088  .  .  .  Open  Hearth 

moS      J    6'II6'755  •  •  •  Bessemer 

I    7,780,872  .  .  .  Open  Hearth 

As  compared  with  the  Bessemer,  its  opera- 
tions are  under  greater  control,  samples  can 
be  taken  at  frequent  intervals  and  thoroughly 
tested,  there  is  much  less  danger  of  over-oxidiza- 
tion and  as  a  whole  its  product  is  more  uniform 

13 


A    STUDY    OF    THE    OPEN    HEARTH 

and  reliable.  The  yield  of  ingots  compared  with 
the  total  of  metal  charged  is  also,  as  compared 
with  the  Bessemer,  higher. 

DESCRIPTION  OF  OPEN  HEARTH  FURNACE 

Inasmuch  as  with  the  exception  of  the  bottom 
lining,  the  furnace  for  both  basic  and  acid  Open 
Hearth  practice  is  identical,  this  description 
applies  to  each,  with  the  exceptions  noted,  and 
assumes  a  producer  gas  fired  furnace. 

The  furnace  consists  of  a  rectangular  bath, 
hearth  or  basin,  open  at  each  end  for  the 
admission  of  gas  and  air  at  the  ports.  This 
hearth  is  arched  by  a  roof  from  9  inches  to  12 
inches  in  thickness.  At  each  end  of  the  furnace 
are  two  checker  chambers,  one  for  the  pre- 
heating or  regeneration  of  the  air,  the  other  of 
the  gas.  Before  starting  the  furnace  a  wood  fire 
is  built  in  one  set  of  chambers  and  after  these 
have  attained  a  dull  red  heat  the  gas  and  air  are 
passed  through  them,  entering  at  one  end  of  the 
furnace,  are  deflected  downward  by  the  direc- 
tion of  the  ports,  unite  in  combustion  over  the 
hearth,  and  the  gases,  the  products  of  combustion, 
leave  the  furnace  through  the  ports  at  the  oppo- 
site end,  passing  downward  through  the  checkers 
or  regenerative  chambers,  there  giving  up  their 
heat  to  the  checkers,  thence  through  the  flues  to 
the  stacks. 

At  frequent  intervals,  say  from  15  to  20 
minutes,  dependent  on  the  quality  and  amount 
of  fuel,  charge,  working  of  furnace,  etc.,  the 


A    STUDY    OF   THE    OPEN   HEARTH 

currents  of  gas  and  air  are  reversed,  now  enter 
ing  the  furnace  at  the  opposite  ends  and  having 
passed  through  the  checker  chambers,  heated  up 
during  the  previous  period,  take  this  stored 
up  heat  to  create  a  more  intense  flame  over 
the  bath.  These  waste  gases  in  turn  pass  out 
through  the  chambers,  giving  up  their  heat. 
This  reversal  is  maintained  with  regularity  until 
the  charge  is  ready  to  tap. 

It  is  evident  that  we  have  here,  practically 
and  theoretically,  a  constant  increase  of  temper- 
ature, for  at  each  successive  reversal  the  gases 
pass  through  and  over  checkers  hotter  than  at 
the  previous  pass,  giving  in  turn  a  more  intense 
heat  in  combustion  and  an  increasing  tempera- 
ture in  the  chambers.  Where  there  is  a  full 
charge  of  cold  stock  at  the  beginning  of  opera- 
tions and  the  fuel  is  poor  in  quality  or  insuffi- 
cient in  quantity,  these  will,  with  the  necessarily 
increased  radiation  as  the  furnace  becomes  hotter, 
keep  the  heats  from  being  unduly  high,  but  in 
general  with  the  furnace  properly  working  and 
with  a  good  supply  of  gas,  there  is  no  difficulty 
in  reaching  and  maintaining  the  desired  tempera- 
ture. The  practical  limit  is  merely  what  the 
brickwork  of  the  furnace  will  stand.  This  tem- 
perature is  controlled  by  proper  regulation  of  the 
valves  admitting  gas  and  air  to  the  flues. 

The  whole  furnace  is  securely  tied  together 
by  heavy  I-beams  or  channels  serving  as  buck- 
stays  and  connected  both  top  and  bottom  by  tie- 
rods  having  turn  buckles,  these  turn  buckles 

15 


A    STUDY    OF    THE    OPEN    HEARTH 

being  adjusted  as  the  furnace  is  heated  up,  thus 
allowing-  for  the  necessary  expansion.  In  size 
the  furnace  varies  with  the  output  desired,  from 
a  1 5 -ton  furnace  or  even  considerably  smaller, 
for  special  steels,  up  to  60  and  75  tons.  Of  the 
newer  furnaces  the  6o-ton  is  probably  the  more 
usual  size,  it  often  producing  up  to  65  or  even  80 
to  90  tons  per  heat,  and  several  75 -ton  furnaces 
(nominally)  are  regularly  taking  off  heats  of  100 
tons  or  over.  As  a  usual  thing,  however,  the 
preference  is  had  for  an  increased  number  of 
units  of  say  50  or  60  tons,  tapping  at  various 
intervals,  as  the  output  of  ingots  can  be  better 
taken  care  of  than  with  units  of  larger  capacity. 

DETAILS  OF  FURNACE 
ROOF 

The  roof  is  invariably  of  silica  brick.  The 
highest  grade  cannot  be  too  good,  as  to  a  very 
great  extent  both  here  and  in  the  ports  the  ton- 
nage of  the  furnace  is  dependent  upon  the  life 
of  the  brick.  The  difference  in  actual  brick  cost 
between  a  mediocre  and  a  high-grade  brick  is 
nothing  as  compared  with  the  losses  due  to 
shutdown  for  necessary  repairs  and  consequently 
decreased  tonnage.  The  roof  is  in  the  majority 
of  cases  9  inches  thick,  made  of  standard  sized 
wedge  and  straight  brick,  but  on  the  larger 
furnaces  is  often  12  or  13^  inches.  Particularly 
in  a  roof  of  large  span  and  low  rise  it  gives 
structurally  a  much  stronger  design,  an  advantage 
in  construction  such  as  this  where  the  roof  is 

16 


A   STUDY    OF   THE    OPEN    HEARTH 

subjected  to  great  and  widely  varying-  stresses 
due  to  temperature  changes  in  the  furnace. 

Assume  that  a  silica  brick  will  wear  or  burn 
down  to  say  3  inches  in  thickness  before  the  roof 
must  be  renewed  (it  will  sometimes  stand  until 
2  inches  or  even  less  remain),  there  then  goes 
to  the  bat  pile  -f  or  33^  per  cent,  of  the  brick, 
while  if  a  12 -inch  roof  is  used  only  T3^  or  25  per 
cent,  is  wasted.  By  far  the  greater  saving,  how- 
ever, comes  in  the  increased  life  of  the  roof  and 
consequent  increased  tonnage. 

As  compared  with  a  roof  12  inches  thick  the 
increased  radiation  from  a  9 -inch  roof  once 
deemed  necessary  to  prevent  the  melting  of  the 
silica  brick,  is  entirely  needless  when  the  roof 
is  constructed  of  the  highest  grade  material,  and 
so  far  as  this  point  is  concerned  it  may  be  any 
desired  thickness.  In  certain  portions  of  the 
furnace  roof  18  to  2o-inch  sections  are  giving 
excellent  results. 

In  the  earlier  types  of  furnace  the  roof  was 
brought  down  very  low  over  the  hearth  with  the 
idea  of  keeping  the  flame  in  closer  contact  with 
it,  but  experience  has  shown  that  if  too  low  the 
roof  is  rapidly  burned  away,  proper  combustion 
is  retarded,  there  not  being  sufficient  room  for 
the  proper  development  of  the  flame,  and  the 
impinging  flame  of  the  ports  playing  almost 
directly  against  the  low  drop  roof,  very  soon 
cuts  the  latter  away.  The  roof  is  usually  now 
built  of  such  ample  height  as  to  remedy  these 
difficulties. 

17 


A   STUDY    OF   THE    OPEN   HEARTH 

In  all  modern  furnaces  the  skew  backs  on 
which  the  roof  arch  rests  are  in  turn  supported 
on  heavy  channels,  a  part  of  the  steel  furnace 
frame.  Thus  the  full  thrust  of  the  arch  is  here 
taken  up,  relieving  the  front  and  back  walls  of 
the  furnace  from  any  other  than  their  own  dead 
weight.  Inasmuch  as  the  front  and  back  walls 
often  require  patching  and  renewal,  the  necessity 
of  thus  supporting  the  roof  is  apparent.  In  the 
old  style  of  furnace  the  giving  way  of  a  wall 
meant  the  failure  of  the  entire  roof. 

A  number  of  furnace  roofs  are  now  con- 
structed on  a  radius  not  only  from  front  to  back 
wall  but  also  arched  longitudinally,  /.  e.,  from 
port  to  port.  This  has  proven  good  practice, 
enabling  the  furnace  to  take  care  of  expansion 
and  contraction  to  good  advantage  and  also 
giving  a  very  strong  construction. 

HEARTH  AND  BOTTOM 

For  proper  operation  it  is  imperative  that  the 
hearth  be  of  such  length  as  to  allow  full  combus- 
tion over  the  bath  proper,  thus  obtaining  the  full 
calorific  value  of  the  flame.  Furthermore,  if  the 
hearth  is  of  insufficient  length  there  will  be 
undue  cutting  of  the  ports  as  the  gases  leave  the 
furnace,  in  some  instances  the  gases  in  reality 
burning  in  the  ports  and  upper  portions  of  the 
checker  work.  This  means  excessive  renewals, 
high  fuel  consumption  and  general  wasteful 
operations.  In  one  instance  on  account  of  the 
defective  proportioning  of  the  furnace,  general 

if 


A    STUDY    OF    THE    OPEN    HEARTH 

repairs  were  necessary  every  300  heats,  while 
with  one  properly  proportioned  1200  heats  is 
easily  attained  in  acid  practice. 

Fifteen  feet  is  usually  considered  the  maxi- 
mum width,  as  furnace  operatives  can  hardly 
throw  the  refractory  material  for  patching  and 
daubing  the  back  wall  a  greater  distance  than 
this.  The  length  will  usually  be  from  2  to  2% 
times  the  width. 

As  to  the  depth  of  the  hearth  proper  as 
finally  lined  up,  it  must  be  the  happy  medium 
between  such  shallowness  as  shall  promote  rea- 
sonably quick  working  of  the  bath  and  a  mainte- 
nance of  proper  thermal  conditions  throughout 
its  mass,  and  of  such  depth  as  will  reduce  the  oxi- 
dization of  metal  to  a  minimum,  avoiding  over- 
burned  metal  and  a  reduced  percentage  of  out- 
put as  compared  with  the  metal  charged.  This 
balance  is  usually  obtained  with  a  depth  of  from 
15  to  20  inches. 

The  entire  bottom  and  hearth  of  the  furnace 
is  built  in  and  supported  by  a  pan  of  heavy 
riveted  steel  plates,  supported  in  turn  on  I-beams 
or  channels  resting  on  piers  and  entirely  inde- 
pendent of  the  regenerators  or  other  parts  of 
the  furnace.  Reasons  for  this  will  be  later 
taken  up. 

MATERIAL    FOR    BOTTOMS 

It  is  here  only  that  there  is  material  difference 
between  the  acid  and  basic  Open  Hearth,  this 
due  to  the  nature  of  the  slags  carried  in  the  acid 

19 


A   STUDY    OF   THE    OPEN   HEARTH 

and  basic  processes  respectively,  and  it  is  from 
the  nature  of  these  that  the  processes  derive 
their  names. 

In  the  acid  process  the  slag  is  made  up  of  the 
silica  sand  adhering1  to  the  pig  metal*  charged 
and  the  silica  due  to  the  oxidization  of  the  silicon 
in  the  pig,  as  well  as  of  the  oxides  of  manganese 
and  iron,  these  oxides  forming  during  the  work- 
ing of  the  charge,  and  were  a  basic  lining  used 
in  the  bottom,  there  would  of  course  be  a  reaction 
between  the  slag  and  lining,  consequently  an  acid 
or  neutral  lining  is  used,  while  for  basic  practice 
a  neutral  or  basic  material  is  necessary  to  avoid 
reaction  between  the  bottom  and  the  slags  ren- 
dered basic  by  the  addition  of  lime  for  the  re- 
moval of  phosphorus  and  sulphur. 

ACID    MATERIALS 

The  only  acid  material  used  is  silica  sand, 
all  acid  furnace  bottoms  being  made  from  it.  A 
natural  sand  is  often  used  containing  various 
percentages  of  silica,  a  typical  analysis  being, 
for  instance: 

Water 24  per  cent. 

Silica     .                   .         .  97.25  per  cent. 

Alumina  and  iron  oxide  .16  per  cent. 

Lime     .         .         .         .  .08  per  cent. 

Magnesia       .         .         .  .39  per  cent. 

Alkalies         .         .         .  .36  per  cent. 

Loss  on  ignition    .         .  .36  per  cent. 

Certain  beach  sands  give  very  good  results, 
and  there  are  also  a  number  of  deposits  in  the 


A    STUDY    OF    THE    OPEN    HEARTH 

West  and  Middle  West,  but  it  is  impossible  to 
predict  by  analysis  alone  the  quality  of  a  given 
sand.  If  of  excessive  purity  there  is  difficulty 
in  properly  setting  it  in  the  furnace,  and  if  the 
impurities  run  too  high,  although  the  sand  will 
then  easily  frit  or  set,  it  is  subject  to  great  ero- 
sion in  the  operation  of  the  furnace  and  will  not 
make  a  sufficiently  hard,  dense  bottom.  The 
physical  characteristics  have  a  wide  bearing  on 
the  question  of  its  adaptability,  and  two  sands  of 
practically  identical  analysis  may  considerably 
differ  as  to  their  suitability  for  bottom  work. 
Often  a  combination  of  two  or  more  sands  will 
secure  the  best  results. 

NEUTRAL    MATERIAL 

Carbon,  while  almost  perfectly  resisting  the 
action  of  the  slag,  is  very  rapidly  destroyed  on 
account  of  the  great  affinity  of  the  metal  for  it. 
It  has  often  been  tried  in  the  form  of  brick,  as 
well  as  rammed  with  tar,  and  although  the  mat- 
ter is  again  and  again  reviewed  by  those  not 
familiar  with  previous  experiments,  its  practical 
use  is  out  of  the  question. 

Bauxite,  a  hydrous  oxide  of  alumina,  anal- 
yzing approximately : 

Silica           .  SiO2  4  to  7  per  cent. 

Iron  peroxide  Fe2O8  3  to  5  per  cent. 

Alumina     .  A18O3  .       60  per  cent. 

Water         .  H8O  .       30  per  cent. 

although  exceedingly  refractory,  is  subject  to 
excessive  shrinkage  at  furnace  temperatures.  It  is 


A    STUDY    OF    THE    OPEN    HEARTH 

very  difficult  to  so  calcine  as  to  entirely  eliminate 
this  shrinkage,  and  when  so  calcined,  all  plasticity 
is  lost  through  loss  of  its  combined  water.  In 
modern  Open  Hearth  practice  it  is  never  used. 

Chromite,  a  sesqui-oxide  of  chromium,  usually 
termed  chrome  ore,  which  has  been  rather  more 
thoroughly  tried  out  abroad  than  in  this  country, 
is  extremely  infusible  and  practically  neutral, 
but  its  infusibility  renders  it  very  difficult  to  set 
or  sinter  thoroughly,  and  it  has  been  found 
practically  impossible  to  so  thoroughly  set  the 
bottom  that  it  will  not  be  subject  to  mechanical 
erosion  rather  than  any  chemical  reaction.  It 
will  analyze  as  follows : 

Sesqui-oxide  of 

chromium    .     Cr2O3  38  to  40  per  cent. 

Alumina      .     A12O3  .    24.5    per  cent. 

Iron  peroxide  Fe2O3  .     17.5    percent. 

Silica  .         .     SiOa  .      3.25  percent. 

Magnesia     .     MgO  .     15       per  cent. 

In  spite  of  its  high  refractoriness  it  has,  when 
selected  with  due  regard  to  its  analysis,  and 
when  properly  prepared,  a  large  and  rapidly 
widening  field  in  daubing  and  patching  around  the 
slag  line,  back  walls,  ports,  jambs,  etc. 

Of  course  a  neutral  bottom  would  be  the  ideal 
one  for  Open  Hearth  practice,  inasmuch  as  any 
change  from  the  basic  to  acid  process,  or  vice 
versa,  could  be  made  without  change  in  the  fur- 
nace, but  as  indicated  above,  the  materials  at  our 
disposition  do  not  allow  a  satisfactory  neutral 
working  bottom. 


A        STUDY         OF        THE         OPEN        HEARTH 
BASIC    MATERIALS 

Lime,  or  calcium  carbonate,  CaCO3,  is,  in  its 
calcined  form,  CaO,  theoretically  an  excellent 
material  for  bottoms,  but  it  is  practically  out  of 
the  question,  due  to  the  rapidity  with  which  it 
slakes  when  exposed  to  air.  When  reheated,  the 
rapid  driving  off  of  the  gas  and  water  reduces 
the  lime  to  a  powder,  in  which  condition  it  is 
rapidly  worn  away. 

Dolomite,  a  magnesian  limestone,  is  one  of 
the  materials  very  commonly  used  for  patching 
bottom,  and  in  some  cases  even  for  the  entire 
bottom,  particularly  by  those  to  whom  its  com- 
paratively low  first  cost  appeals,  but  it  is  open  to 
the  same  objection  as  lime,  only  in  a  lesser  de- 
gree, i.  e.,  slaking  on  exposure  to  the  atmos- 
phere, and  if  a  stock  is  more  than  ten  days  to 
two  weeks  old  this  becomes  an  important  factor. 
Of  course  where  the  plant  calcines  its  own  dolo- 
mite this  is  a  less  important  consideration.  Fur- 
thermore, it  is  impossible  to  so  set  a  dolomite 
bottom  that  it  shall  be  as  dense  and  vitreous  as 
magnesite,  and  in  spite  of  most  watchful  care 
portions  of  the  bottom  will  from  time  to  time 
become  detached  and  float;  in  fact,  within  the 
last  two  or  three  days  of  this  writing  we  have 
reports  advising  that  the  entire  bottom  in  each 
of  two  furnaces  has  floated.  In  a  dolomite  bot- 
tom where,  through  erosion  or  absorption  of 
metal,  a  hole  or  depression  is  once  started,  dis- 
integration progresses  with  much  more  rapidity 
than  with  magnesite,  and  there  is  considerably 

23 


A    STUDY    OF    THE    OPEN    HEARTH 

more  liability  of  serious  breakouts.  A  fairly 
representative  analysis  of  dolomite  is  as  follows : 

Silica 5.52  per  cent. 

Alumina  and  iron  .  3. 74  per  cent. 
Calcium  ....  29.20  per  cent. 
Magnesia  .  .  .  .17.31  per  cent. 
Loss  on  ignition  .  .  43.82  per  cent. 

In  a  number  of  instances  the  absorption  of  the 
impurities  from  the  dolomite  has  proven  an  ex- 
ceedingly serious  matter  in  the  manufacture  of 
high  grade  steels  and  has  resulted  in  an  increased 
use  of  magnesite.  Dolomite  sets  somewhat  more 
rapidly  than  magnesite. 

Magnesium  carbonate  (MgCOs),  when  calcined 
to  the  oxide,  MgO,  commercially  known  as  mag- 
nesite, is  unquestionably  the  best  material  for 
Open  Hearth  bottoms,  and  all  original  bottoms 
are  now  installed  with  it.  Even  by  those  using 
a  large  percentage  of  dolomite  in  repairing,  it 
is  admitted  to  be  the  best  material  available,  ab- 
solutely the  only  argument  in  favor  of  dolomite 
being  its  low  first  cost.  The  well-known  Aus- 
trian magnesite  of  the  following  approximate 
analysis 

Silica       .         .  SiO2  .  2.84     per  cent. 

Alumina          .  A18O3  .  .929  per  cent. 

Iron  peroxide  Fe3O3  .  8.571  percent. 

Lime       .         .  CaO  .  1.120  percent 

Magnesia         .  MgO  .  85.32     percent. 

Carbon  dioxide  CO3  .  .50     percent. 

gives  such  a  proportion  of  iron,  etc.,  as  makes 
the  material  set  in  the  furnace  bottom,  forming 


A    STUDY    OF   THE    OPEN    HEARTH 

a  hearth  of  maximum  density,  subject  to  mini- 
mum erosion  by  the  metal,  and  practically  un- 
affected by  the  slags.  Furthermore,  on  indefinite 
exposure  to  the  atmosphere  almost  no  deteri- 
oration takes  place,  while  with  a  dolomite 
bottom  under  like  conditions,  should  furnace 
shut-down  occur,  the  bottom  would  of  necessity 
be  renewed.  The  large  deposits  of  Austrian 
magnesite  insure  ample  supply  for  years  to 
come. 

Grecian  magnesite  has  been  used  as  a  bottom 
material,  but  on  account  of  its  high  refractori- 
ness there  is  difficulty  in  fusing  it  in  place,  it 
being  necessary  to  introduce  impurities  in  the 
way  of  silica,  clay,  or  oxide  of  iron  in  amounts 
sufficient  to  reduce  its  refractoriness.  The  re- 
sultant is  too  variable  a  quantity  to  give  reliable 
results,  and  Grecian  magnesite  is  very  seldom 
employed. 

CONSTRUCTION    OF    ACID    BOTTOM 


In  the  center  of  the  furnace  wall,  near  the 
base  on  the  tapping  side,  is  left  an  opening  from 
15  to  20  inches  square,  arched  over  with  silica 
brick.  Into  this  opening  is  inserted  a  tapered 
plug  the  size  of  the  finished  tap  hole.  Around 
the  plug  is  rammed  ganister,  and  the  plug  being 
withdrawn  the  hole  is  almost  filled  from  the 
charging  side  with  lump  anthracite  coal,  the 
remainder  being  rammed  with  fire  clay  from  the 


A    STUDY    OF   THE    OPEN    HEARTH 

outside,  the  furnace  then   being  ready  to  make 
bottom. 


Directly  on  the  steel  shell  or  pan  forming  the 
bottom  is  placed  from  one  to  three  courses  of 
silica  or  clay  brick,  preferably  silica,  and  at  the 
sides  and  ends  of  the  furnace  a  number  of  addi- 
tional courses  stepped  up  as  in  the  illustration, 
showing  magnesia  brick  in  the  basic  Open  Hearth, 
page  ii.  The  thickness  of  the  sand  bottom 
proper  will  then  be  approximately  the  same  over 
the  entire  basin-shaped  hearth.  Over  this  brick  is 
sometimes  spread  a  thin  layer  of  sandstone  or 
granite  clippings,  while  this  is  by  no  means  in- 
variable. The  gas  is  then  turned  on,  the  heat 
gradually  increased  until  the  chips  begin  to 
soften  or  sinter,  when  a  thin  layer  of  sand,  say 
one-half  to  three-quarters  of  an  inch,  is  spread 
evenly  over  the  hearth  and  the  heat  maintained 
at  sufficient  temperature  to  glaze  over  this  coat- 
ing of  sand.  Another  layer  is  then  spread  and 
the  process  repeated  until  the  entire  bottom  is 
built  up  to  a  thickness  of  15  to  20  inches  of  this 
vitreous,  glassy  structure.  The  bottom  is  run 
well  up  the  side  wall  to  a  distance  of  at  least  a 
foot  above  the  slag  line. 


In  order  to  thoroughly  consolidate  the  bot- 
tom, it  is  usual  to  run  what  is  termed  a  ''wash- 
heat."  This  consists  merely  in  melting  a  charge 

26 


A    STUDY    OF    THE    OPEN    HEARTH 

of  acid  open  hearth  slag  and  thoroughly  washing 
down  the  banks  of  the  furnace  with  it. 

CONSTRUCTION    OF    BASIC    BOTTOM 
TAP    HOLE 

This  is  made  in  much  the  same  way  as  with 
an  acid  bottom,  except  that  the  hole  is  arched 
usually  with  magnesia  brick  and  magnesite, 
rendered  slightly  plastic  with  anhydrotis  tar 
rammed  around  the  form,  or  ground  chrome  ore 
may  be  used  instead  of  the  magnesite.  The 
chrome  ore  when  of  proper  analysis  and  properly 
set  undoubtedly  makes  the  best  material  for  tap- 
ping holes,  the  hole  itself  being  filled  with  mag- 
nesite or  magnesite  and  dolomite  mixed.  This 
is  tamped  well  into  place  by  ramming  against 
a  rabble  held  against  the  inside  of  the  furnace. 


On  the  steel  shell  forming  the  bottom  of 
the  furnace  are  placed  two  or  three  courses  of 
first  quality  clay  brick,  then  three  or  more 
courses  of  magnesia  brick,  the  latter  being  car- 
ried well  up  the  banks  of  the  furnace  and  stepped 
off  as  in  the  case  of  silica  brick  with  the  acid 
furnace.  Often  a  course  of  chrome  brick  is 
inserted  between  the  clay  and  the  magnesia  brick, 
and  sometimes  no  clay  brick  whatever  are  used 
here,  merely  the  magnesia  brick.  The  mag- 
nesia brick  serve  to  greatly  retard  the  breaking 
through  of  the  metal,  should  the  furnace  bottom 

27 


A    STUDY    OF   THE    OPEN    HEARTH 

proper  be  cut  through,  and  usually  allows  suffi- 
cient warning  so  that  the  charge  may  be  tapped 
off  before  the  metal  actually  breaks  out. 

In  this  connection  it  is  in  a  number  of  foreign 
plants  the  custom  to  use  a  very  much  larger 
proportion  of  magnesia  brick  in  the  bottom  than 
in  this  country,  a  comparatively  small  part  only, 
say  6  to  8  inches,  being  made  up  of.  the  sintered 
grain  magnesite.  The  idea  is,  of  course,  that 
the  brick  are,  due  to  their  density  and  the  fact 
that  they  have  previously  been  burned  at  very 
high  temperatures,  more  resistant  to  the  passage 
of  metal  and  slag.  This  is  undoubtedly  true. 
The  question  arises,  however,  as  to  how  much 
this  is  offset  by  the  necessary  increase  of  joints, 
always  an  element  of  weakness  where  anything  is 
encountered  as  fluid  as  molten  steel  and  slag  at 
the  temperature  of  the  open  hearth  furnace.  So 
far  as  economy  in  the  original  installation  is  con- 
cerned, there  is  probably  little  to  choose,  inas- 
much as  although  the  brick  are  naturally  expen- 
sive, yet  the  fuel  costs  in  setting  an  entire  bottom 
of  grain  magnesite  are  also  high. 

Directly  on  the  magnesia  brick  is  spread  in  a 
thin  layer  the  grain  magnesite.  This  is  some- 
times mixed  with  hot  tar  previous  to  its  applica- 
tion to  render  it  plastic,  although  this  is  not  the 
usual  custom.  In  order  to  hasten  its  setting,  from 
5  to  15  per  cent  of  basic  cinder  is  often  introduced, 
the  mixing  being  done  on  the  charging  floor  by 
shoveling,  much  as  cement  and  sand  are  mixed, 
for  instance,  one  shovel  of  finely  ground  cinder  to 


A   STUDY    OF   THE    OPEN    HEARTH 

five  of  magnesite.  The  magnesite  is  then  fused  on 
the  magnesia  brick  bottom  in  layers,  in  exactly 
the  same  way  as  is  the  sand  on  the  acid  furnace 
bottom,  building  up  the  front  and  back  walls  well 
above  the  slag  line.  With  the  furnace  at  melting 
heat,  the  material  becomes  pasty,  and  with  a  rab- 
ble it  is  a  comparatively  easy  matter  to  shape  the 
bottom  and  sides  as  desired. 

WASH    HEAT 

A  wash  heat  of  basic  slag  or  of  roll  scale  is 
charged,  allowing  it  to  melt  and  soak  well  into 
the  bottom,  tapping  off  the  remainder.  This  not 
only  prevents  the  later  absorption  of  metal  but 
considerably  increases  the  density  of  the  hearth. 

FRONT    AND     BACK    WALLS 

In  the  acid  furnace  the  front  and  back  walls 
are  throughout  of  silica  brick ;  in  the  basic,  are 
silica  from  a  few  courses  above  the  slag  line  up, 
but  below  this  of  magnesia  brick.  It  was  at  one 
time  almost  universally  the  custom  to  insert 
between  the  basic  magnesia  brick  in  the  front 
and  back  walls  and  the  acid  silica  brick  one  or 
two  courses  of  neutral  chrome  brick.  However, 
many  Open  Hearths  are  now  built  and  with  ap- 
parent satisfaction  without  this  neutral  course, 
inasmuch  as  at  the  temperatures  usually  en- 
countered in  Open  Hearth  practice,  there  is  little 
or  no  fluxing  action  between  the  magnesia  and 
silica  brick.  However,  it  is  unquestionably  good 
practice  to  use  chrome  brick  as  indicated,  as  it  is 

29 


A    STUDY    OF    THE    OPEN    HEARTH 

in  effect  an  insurance  against  trouble  due  to 
chemical  action,  should  the  heats  run  consider- 
ably above  normal  temperatures,  as  they  are  %of 
course  liable  to  do,  and  a  number  of  instances 
have  been  recorded  where  serious  trouble  has 
occurred  due  to  omission  of  the  neutral  brick. 

In  basic  practice  the  walls  should  be  daubed 
with  chrome  ore  finely  ground,  this  preferably 
extending  entirely  to  the  skew  line.  It  is  an 
economy,  as  it  almost  wholly  protects  these 
walls  from  the  action  of  the  gases  laden  with 
dust,  slag,  limestone  and  iron  oxide  spray  which 
otherwise  very  rapidly  erodes  them.  Here  again  ' 
not  all  chrome  ores  are  suitable,  if  too  refractory 
the  ore  merely  dries  and  rolls  away,  a  suitable 
ore,  however,  shows  marked  plasticity  and 
remains  in  place  until  thoroughly  set. 

BULKHEADS 

The  mass  of  brick  forming  the  ends  of  the 
furnace  hearth  is  often  termed  the  "bulkhead," 
and  at  one  time  it  was  the  custom  to  build 
this  in  solid,  of  silica  brick  except  for  the  facing 
of  magnesia  brick  somewhat  above  the  height 
of  the  slag  line  in  the  basic  Open  Hearth. 
However,  in  such  a  mass  there  is  comparatively 
little  radiation  and  the  bulkhead  very  rapidly 
burned  away.  In  modern  furnaces  this  construc- 
tion is  replaced  by  a  steel  frame  supporting  the 
end  walls  of  the  hearth,  so  that  comparatively 
few  courses  of  brickwork  are  necessary,  the  bulk- 
head then  being  practically  air  cooled.  This 

30 


A    STUDY    OF    THE    OPEN    HEARTH 

simple  expedient  has  effected  great  savings  not 
j  only  in  brick  costs  but  in  the  operation  of  the 

furnace.     In  the  best  basic  practice,  it  is  now  the 

custom  to  face  the  entire  bulkhead  of  the  furnace 
j  up  to  the  ports  with  magnesia  brick,  or  to  bank 

it  with  lump  or  ground  chrome  ore,  this  giving 
!  in  some  instances  fifteen  or  sixteen  times  the  life 

of  silica  brick. 

PORTS 

These  are  the  openings  through  which  the  gas 
and  air  are  admitted  to  the  furnace,  and  the 
proper  operation  of  the  furnace  is  nowhere  more 
dependent  on  good  design  than  here.  In  the 
ports  originate  by  far  the  larger  proportion  of 
Open  Hearth  furnace  troubles,  and  even  when 
perfectly  designed  as  to  size,  arrangement  and 
alignment,  it  is  a  difficult  matter  to  keep  them 
so.  One  or  the  other  end  of  the  furnace  is 
continuously  subject  to  the  outgoing  rush  of 
incandescent  gases  laden  with  particles  of  ore, 
limestone,  slag,  etc.,  and  at  a  comparatively 
high  velocity  due  to  diminution  of  area  from  that 
over  the  hearth  to  that  of  the  ports.  This  action 
tends  to  cut  back  the  ports  very  rapidly.  In  a 
large  number  of  cases  there  are  two  gas  and  two 
air  ports  at  each  end  of  the  furnace,  although  this 
is  varied  by  one  gas  and  two  air,  or  two  gas 
and  three  air,  and  in  the  majority  of  the  large 
modern  furnaces,  one  gas  and  one  air  port. 
Whatever  may  be  the  number,  they  are  so 
arranged  that  the  air,  being  heavier,  shall 

31 


A    STUDY    OF    THE    OPEN    HEARTH 

enter  above  and  outside  the  gas,  the  two  then 
deflected  downward  by  the  alignment  of  the 
ports,  spread  and  mingle  at  the  port  ends,  com- 
bustion there  taking  place  and  the  flame  is  dis- 
tributed over  the  entire  bath  of  metal. 

The  air  being  above  and  outside  the  gas,  keeps 
the  most  intense  heat  away  from  the  roof,  and 
front  and  back  walls,  thus  preventing  the  cutting 
action  of  the  flame  which,  if  directed  against  the 
roof,  very  rapidly  burns  it  away.  In  this  position 
also  not  only  do  the  gas  and  air  naturally  mingle 
on  account  of  their  relative  specific  gravities, 
but  the  gas  being  lower,  keeps  the  current  of 
heated  air  from  directly  impinging  upon  the 
stock,  which  if  allowed  to  occur  would  produce 
undue  oxidization  of  the  metal.  The  alignment 
is  usually  such  as  will  make  the  gas  and  air  meet 
slightly  above  the  surface  of  the  metal,  approxi- 
mately 3  feet,  although  it  is  often  so  designed 
that  this  will  be  at  a  point  considerably  higher, 
say  4  or  5  feet,  but  if  the  latter  height  is  exceeded, 
there  is  a  tendency  for  the  flame  to  cut  away  the 
roof  too  quickly,  and  if  lower  than  approximately 
3  feet,  combustion  is  somewhat  retarded  by  the 
gases  being  chilled  by  the  cold  stock,  and  full 
development  of  flame  prevented. 

The  importance  of  the  details  of  port  construc- 
tion can  be  most  easily  comprehended  by  realiz- 
ing that  the  gas  and  air  ports  together  with  the 
down-takes  (vertical  flues  leading  from  the  ports 
to  the  gas  and  air  chambers)  form  merely  an 
ordinary  gas  burner  on  a  large  scale,  and  from 

32 


A   STUDY    OF   THE    OPEN   HEARTH 

this  point  of  view,  the  necessary  and  frequent 
adjustments  as  to  the  admission  of  gas  and  air 
appear  very  simple.  As  illustrating  how  compar- 
atively small  a  matter  may  cause  trouble  in  the 
operation  of  the  furnace  through  port  troubles,  a 
certain  Open  Hearth  roof  burned  out  after  15  or 
1 6  heats,  the  trouble  occurring  in  one  spot  in  the 
roof.  On  investigation  this  was  found  due  to  a 
silica  bat  which  had  been  left  lying  in  the  gas 
port.  The  gas  impinging  on  this  brick,  had  been 
thrown  in  an  eddy  directly  on  the  roof,  causing 
the  hot  spot  referred  to.  After  the  removal  of 
the  bat  there  was  no  further  trouble. 

The  ports  and  blocks,  that  is  the  mass  of 
brickwork  forming  the  end  of  the  furnace 
through  which  the  ports  extend,  are  ordinarily 
built  up  of  silica  brick,  but  due  to  the  rapidity 
with  which  these  ports  cut  away,  numberless 
schemes  have  been  tried  for  lengthening  the  life 
of  this  portion  of  the  furnace.  Among  these  is 
the  water-cooled  port  constructed  of  bronze  cool- 
ing plates,  a  type  similar  to  that  in  ordinary  use 
in  blast  furnace  practice,  with  these  plates  form- 
ing the  division  wall  between  the  gas  and  air 
ports,  protected  by  one  or  more  courses  of  mag- 
nesia or  chrome  brick.  This  has  given  in  many 
cases  very  good  results,  affording  much  longer 
life  than  the  ordinary  one. 

There  are  a  number  of  other  types  of  water- 
cooled  ports,  in  some  instances  constructed  by 
imbedding  water  cooled  pipes  in  the  port  arch,  this 
arch  being  made  of  ground  magnesite  or  of 

33 


A    STUDY    OF   THE    OPEN    HEARTH 

ground  chrome  ore  rammed  over  .forms.  In  other 
cases,  the  arch  is  supported  directly  on  water 
cooled  pipes. 

Instead  of  making"  the  port  of  silica  brick, 
some  have  used  forms  rammed  with  ganister, 
with  a  small  quantity  of  binding  clay,  fusing  it  in 
place.  This  is  an  improvement  in  so  far  as  it 
does  away  with  the  joints  of  the  brick  work, 
always  an  element  of  weakness,  but  in  the 
majority  of  instances  has  not  been  found  a  sub- 
stantial saving,  as  it  burns  back  in  the  same 
manner  as  will  the  ordinary  port.  By  far  the 
most  satisfactory  method  of  extending  the  life 
seems  to  be  to  pave  them  with  magnesia  brick  or 
fine  ground  chrome  ore,  and  also  daubing  the 
face  of  the  port  with  this,  its  plasticity  enabling 
it  to  remain  in  place  until  sufficiently  set. 

REGENERATORS 

As  to  the  location  of  the  gas  and  air  chambers 
or  regenerators,  these  are  now  nearly  always 
placed  entirely  independent  of  the  furnace  body 
proper.  Formerly  the  chambers  were  directly 
under  the  body  of  the  furnace,  the  furnace  rest- 
ing on  them,  and  old  furnace  men  still  claim 
that  with  such  construction  a  furnace  works 
somewhat  quicker  than  with  the  present  type, 
but  there  are  many  decided  objections.  In  the 
first  place,  with  the  furnace  resting  directly  on 
the  arches  of  the  chambers,  where  there  is  neces- 
sarily more  or  less  distortion  due  to  changes  in 
temperature,  cracks  are  very  easily  opened  up 

34 


A   STUDY    OF   THE    OPEN    HEARTH 

both  in  the  furnace  and  chamber  walls,  and  it  is 
much  more  difficult  to  keep  the  construction 
gas  and  air  tight.  Second,  any  breakout  allows 
the  metal  from  the  hearth  to  run  directly  into 
the  checkers,  filling  them  up  and  making  an 
enormous  amount  of  work  before  the  furnace 
can  be  again  put  in  commission.  Third,  repairs 
to  one  or  the  other,  i.  e.,  furnace  proper  or 
regenerators,  cannot  be  as  well  taken  care  of. 

As  to  the  proportions  of  air  and  gas  chambers 
there  is  much  discussion,  in  some  of  the  older 
types  they  are  made  of  practically  the  same 
size,  but  in  all  newer  furnaces  the  air  is  consider- 
ably larger,  roughly,  the  proportion  being  at 
least  i}/3  to  i.  This  is  logically  correct  as  regards 
the  quantities  required  for  proper  combustion  of 
the  gas  and  air,  and  furthermore,  the  tempera- 
ture of  the  air  has  considerably  more  bearing  on 
the  final  temperature  of  combustion  than  has  the 
gas.  The  exact  proportion  of  the  two,  however, 
is  not  so  important  as  that  they  be  ample  in  size, 
the  cubical  contents,  however,  being  by  no  means 
the  only  factor  determining  the  proper  working 
of  this  part  of  the  furnace.  In  the  best  practice, 
the  tendency  is  to  have  the  chambers  of  greater 
height  rather  than  secure  the  same  volume  with 
a  low  arch  and  increased  length.  This  is  due  to 
the  fact  that  the  gases  tend  to  rise  and  a  more 
uniform  draft  is  secured  by  having  a  sufficient 
quantity  of  checkers  in  the  vertical  direction 
rather  than  by  making  the  gases  travel  for  a 
considerable  distance  through  long  passages. 

35 


A    STUDY    OF   THE    OPEN    HEARTH 

Furthermore,  the  retardation  due  to  the  friction 
of  air  and  gas  does  not  become  as  important  a 
factor.  Roughly,  the  height  should  be,  for  a 
6o-ton  furnace,  from  13  to  18  feet  and  in  cubic 
capacity,  a  very  common  allowance  is  90  cubic 
feet  per  ton  of  steel. 

At  the  bottom  of  the  regenerators  are  usually 
placed  what  are  termed  "Regenerator"  or 
"Girder"  tile,  these  tile  forming  flues  extending 
the  complete  length  of  the  regenerators.  On  these 
tile  are  built  up  the  standard  9 -inch  or  small 
checker  brick  into  a  series  of  vertical  flues  hav- 
ing openings  of  3^  to  4  inches.  Other  things 
being  equal,  the  efficiency  of  the  chambers  is  de- 
pendent upon  the  amount  of  surface  of  checkers 
heated,  and  consequently  giving  up  their  heat, 
but  it  is  perfectly  possible  to  over-do  this  matter, 
inasmuch  as,  if  the  openings  between  the  brick 
are  too  constricted  they  very  rapidly  clog,  due  to 
accumulations  of  flue  dust,  etc.,  carried  over  by 
the  gases,  this  meaning  excessive  shutdowns  for 
repairs  and  cleaning.  There  has  also  been  used 
in  a  number  of  furnaces  a  large  checker, 
ioj4  x  4^  x  4^  inches,  this  being  used,  how- 
ever, only  in  chambers  whose  dimensions  are 
especially  designed  for  it.  The  advantage  claimed 
is  that  with  a  brick  of  such  size  it  can  be  used 
many  times  over,  this  effecting  a  considerable 
saving  in  brick  costs. 

On  the  other  hand,  many  who  have  gone  into 
the  matter  very  thoroughly,  claim  that  the  brick 
is  of  such  size  that  the  interior  portion  does  not 

36 


A    STUDY    OF   THE    OPEN    HEARTH 

become  thoroughly  heated  by  the  time  each 
reversal  is  made ;  in  other  words,  that  a  certain 
center  portion  of  the  brick  is,  while  taking  up 
the  space  in  the  regenerative  chambers,  inactive, 
and  that  with  the  same  contents  and  with  the 
same  cubic  capacity  in  the  checkers,  greater 
efficiency  can  be  secured  by  increasing  the 
regenerative  surface,  using  smaller  sizes,  such  as 
9-inch  Straight  and  Standard  Checker. 

As  to  the  kind  of  brick  used  for  checkers, 
there  are  many  variations  suited  to  special  con- 
ditions. In  probably  a  majority  of  cases  a  first 
quality  clay  brick  is  used  throughout.  Still 
others  use  first  quality  for  all  except  the  top  ten 
or  twelve  courses  which  are  laid  with  silica  brick, 
a  constantly  increasing  number  using  silica  brick 
throughout.  These,  it  is  claimed,  become  choked 
very  much  less  readily  than  do  the  clay  brick,  the 
carbon  coating  not  seeming  to  penetrate  and 
adhere  to  the  brick  as  is  the  case  with  the  clay 
brick.  They  often  give  several  times  the  life  of 
clay  brick. 

In  other  instances,  furnace  men  have 'found  a 
marked  benefit  in  the  use  of  magnesia  brick  for 
the  top  five  or  six  courses,  the  claims  for  them 
being  the  same  as  for  silica,  except  that  they  are 
better  even  than  the  latter.  Furthermore,  mag- 
nesia and  silica  brick  on  top  courses  exert  a 
marked  influence  on  the  quick  working  of  the 
furnace,  enabling  the  heats  to  be  taken  off  some- 
what faster.  Others  have  applied  a  thin  wash 
of  very  finely  powdered  chrome  ore  to  the 

37 


A    STUDY    OF   THE    OPEN    HEARTH 

checkers,  this  rendering-  them  less  affected  by 
the  caking  of  slag,  soot,  etc.  There  is  absolutely 
no  question  but  what  often  a  great  economy 
in  the  operation  of  the  furnace  can  be  effected  by 
the  substitution  of  a  first  quality  grade  of  checker 
brick  for  the  inferior  material  sometimes  used. 
The  walls  of  the  chambers  should  be  made  of 
first  quality  clay  or  silica  brick,  it  often  being 
advantageous  to  make  the  arches  of  silica  brick, 
especially  where  the  flues  open  into  the  chambers. 
Silica  brick  of  course  expand  and  tend  to  hold 
everything  tight  as  the  furnace  is  heated  up.  It 
also  is  considerably  more  refractory  and  will 
give  much  longer  life.  Where  with  the  use  of 
silica  brick  there  is  danger  of  spawling,  due  to 
sudden  changes  of  temperature,  it  is  found  of 
great  advantage  to  use  an  inner  course  of  clay 
brick,  laying  the  silica  directly  over  this  course. 
The  silica  brick  then  has  opportunity  to  become 
gradually  heated  and  is  in  fact  thoroughly 
annealed  before  the  clay  brick  burn  away  and 
the  silica  is  exposed  to  the  hot  gases. 

SLAG    POCKETS 

The  slag  pockets,  which  are  virtually  but  en- 
largements of  the  flues  leading  from  the  checker 
chambers  to  the  uptakes  and  ports,  are  merely  to 
intercept  the  fine  particles  of  limestone,  slag,  ore, 
etc. ,  carried  over  by  the  gases  in  their  passage  to 
the  chambers.  They  also  serve  to  take  the  slag, 
should  the  furnace  boil  or  froth  excessively. 
Careful  attention,  however,  will  usually  keep 

38 


A   STUDY    OF   THE    OPEN    HEARTH 

such  frothing-  down  to  a  minimum  by  opening-  the 
doors  and  thus  allowing  the  bath  to  cool  slightly. 
By  use  of  slag  pockets  is  avoided  the  constant 
cleaning  out  of  checkers  and  possible  entire  stop- 
page of  the  furnace,  should  the  slag  boil  over  into 
the  gas  ports.  They  are  so  arranged  with  clean- 
out  doors  as  to  be  very  rapidly  emptied  without 
undue  delay  in  furnace  operation. 

UPTAKES    OR    VERTICAL    FLUES 

These  lead  from  the  ports  to  the  slag  pockets. 
They  are  usually  lined  with  first  quality  clay 
brick,  but  it  is  coming  to  be  more  and  more  the 
practice  to  line  them  for  the  upper  half  or  even 
the  entire  height  with  silica  brick,  and  in  some 
instances  it  has  been  advisable  to  line  with  mag- 
nesia brick,  especially  directly  back  of  the  port 
where  the  gases  impinge  against  the  back  wall. 

HORIZONTAL    FLUES 

Horizontal  flues,  a  continuation  of  the  up- 
takes, are  the  passages  leading  from  the  slag 
pockets  to  the  checker  chambers,  and  from  the 
checker  chambers  to  the  stack. 

GAS    AND    AIR    VALVES 

Gas  and  air  are  admitted  to  the  flues  by  a 
simple  form  of  throttle  valve.  In  addition  to  this 
there  is  a  reversing  valve  by  which  is  controlled 
the  reversal  of  the  current  through  the  two 
sets  of  checker  chambers.  The  reversal  valve 
in  most  common  use  is  the  old  Siemens  or 

39 


A    STUDY    OF    THE    OPEN    HEARTH 

"butterfly"  valve,  and  this  is  still  often  installed. 
There  have  been  a  number  of  improvements  on  it. 
In  any  type  of  reversing  valve,  the  valve  casing 
encloses  three  openings,  one  to  the  stack  and  one 
each  to  the  two  chambers,  gas  and  air.  The 
4  *  butterfly"  valve  has  to  recommend  it  its  ex- 
treme simplicity  of  installation  and  operation  as 
well  as  low  first  cost.  Operating  against  it,  how- 
ever, is  the  fact  that  there  is  often  considerable 
trouble  due  to  warping  of  the  valve  occasioned 
by  hot  gases  on  one  side  and  comparatively  cool 
gases  on  the  other.  Although  the  temperature 
of  the  gases  on  their  way  to  the  stack  is  nor- 
mally only  from  400  to  700  degrees  Fahrenheit, 
yet  at  times  when  the  furnace  is  not  operating 
properly,  the  heats  will  rise  considerably,  even  to 
from  1000  to  1200  degrees  Fahrenheit.  Attempts 
have  been  made  to  remedy  this  by  water-cooling 
the  valve,  but  without  great  success.  There  is 
also  at  times  leakage  at  the  valve  seat  due  to  the 
deposit  of  soot  and  tar  at  the  joints,  which  pre- 
vents the  valve  from  closing  tightly.  The  above 
points,  as  well  as  troubles  from  cracking  of  the 
cast  iron  box  enclosing  the  valve,  have  induced 
the  improvements  made  in  the  various  types  of 
water-sealed  valves. 

DAMPERS 

If  the  furnace  were  always  working  properly 
and  the  chambers  entirely  free  and  open  as  at  the 
beginning  of  a  run,  there  would  be  comparatively 
small  necessity  for  dampers,  but,  as  often  happens, 

40 


A    STUDY    OF   THE    OPEN   HEARTH 

the  chambers  become  partially  choked,  due  to  the 
accumulation  of  dust  and  soot,  so  that  in 
order  to  effect  an  even  distribution  of  heat  it  is 
necessary  to  damper  down,  otherwise  one  cham- 
ber will  work  considerably  hotter  than  another. 
The  damper  is  merely  a  rectangular  plate  loosely 
fitting  in  a  frame  set  in  the  flues,  this  plate 
sliding  in  suitable  grooves. 

STACKS 

It  is  important  that  the  stack  have  ample  draft, 
it  being  an  easy  matter  to  damper  down,  but  if 
the  draft  is  insufficient,  proper  working  of  the 
furnace  cannot  be  secured. 

SPECIAL    FURNACES 
TILTING    OR    ROLLING    FURNACE 

The  tilting  or  rolling  furnace  differs  from  the 
ordinary  stationary  type  in  that  the  entire  fur- 
nace body  may  be  rotated  or  tilted  through  a 
considerable  arc,  thus  pouring  the  entire  heat  or 
any  portion  of  it  at  any  stage  of  the  process. 
This  flexibility  in  operation  is  often  of  great 
value. 

In  one  type  the  entire  furnace  body  between 
ports  revolves  on  a  nest  of  rollers,  the  axis  of 
revolution  being  coincident  with  a  line  drawn 
through  the  center  of  the  ports,  thus  enabling 
the  gas  and  air  to  be  kept  on  regardless  of  the 
position  of  the  furnace. 

In  another  type  the  furnace  in  pouring,  rocks 
or  tilts  away  from  this  axis,  thus  breaking  the 

41 


A    STUDY    OF   THE    OPEN    HEARTH 

connection  with  the  ports,  the  gas  and  air  neces- 
sarily being  cut  off  with  the  furnace  in  pouring 
position. 

These  furnaces  do  away  with  a  great  portion 
of  the  tap  hole  troubles,  the  tap  hole  being  above 
the  metal  and  slag  lines  with  the  furnace  in  the 
normal  position,  and  it  is  consequently  only 
necessary  to  fill  the  tap  hole  with  a  very  light 
tamping.  They  also  enable  the  melter  to  thor- 
oughly drain  the  furnace  bottom  of  any  slag  or 
metal,  it  being  in  the  stationary  furnace  often  a 
difficult  matter  to  rabble  or  splash  out  all 
depressions,  and  any  portion  of  the  heat  left  in 
such  a  hole  very  soon  tends  to  permeate  and 
disintegrate  the  surrounding  bottom. 

With  the  furnace  tipped  or  rotated,  the  back 
wall  being  much  nearer  the  horizontal  plain,  this 
wall  may  be  patched  with  bottom  mixture,  and 
this  patching  extended  much  higher  than  on  the 
stationary  furnace,  as  the  material  will  naturally 
adhere  until  set  in  much  larger  quantities  than 
is  the  case  with  the  almost  vertical  back  wall  of. 
the  ordinary  type. 

Where  there  is  excessive  frothing  so  that  the 
slag  tends  to  flow  out  the  doors,  the  furnace 
may  be  tipped,  thus  keeping  the  metal  away  from 
the  working  doors.  In  one  type  of  tilting  or 
rolling  furnace,  any  excess  of  slag  is  allowed  to 
run  out  through  small  holes  in  the  bottom  of  the 
port  openings. 


42 


A    STUDY    OF   THE    OPEN    HEARTH 

CHAPTER   II 

FUELS 

The  fuels  to-day  in  use  in  Open  Hearth  prac- 
tice are  natural  gas,  artificial  gas  and  oil. 

NATURAL     GAS 

By  far  the  best  and  most  satisfactory  from 
every  point  of  view  is  natural  gas,  but  this  of 
course  is  restricted  within  a  comparatively  small 
area.  Its  advantages  aside  from  its  cheap- 
ness where  available,  lie  in  its  higher  calorific 
value,  with  consequent  increased  tonnage  of  the 
furnace ;  its  purity,  there  being  no  sulphur,  etc. , 
to  be  carried  over  and  absorbed  by  the  steel ;  and 
its  cleanliness  and  convenience  in  operation,  it 
requiring  no  heating  previous  to  its  introduction 
to  the  furnace.  It  is  also  very  constant  in  quality 
and  the  furnace  can  be  in  every  way  operated  to 
the  best  advantage. 

When  natural  gas  was  first  introduced  it  was 
attempted  to  run  it  through  the  gas  chambers 
to  preheat  it  in  the  same  way  as  producer  gas, 
but  it  was  found  that  due  to  the  high  percentage 
content  of  hydro-carbons,  the  heavier  hydro- 
carbons deposited  on  the  checker  walls  a  vitreous 
glassy  coke  which  very  soon  clogged  the  check- 
ers and  interfered  with  the  regenerative  effect 
of  the  checker  work. 

Although  artificial  gas  is  far  more  generally 
of  importance,  due  to  the  restricted  area  in  which 
natural  gas  is  available,  yet  in  some  compara- 
tively recent  years  nearly  50  per  cent,  of  the 

43 


STUDY    OF   THE    OPEN   HEARTH 


Open    Hearth    tonnage    has    been    made    with 
natural  gas. 

The  following  average  analyses  of  natural  and 
producer  gas  will  show  very  clearly  the  reasons 
for  the  superiority  of  the  former: 


Percentages 

Constituent 

Formula 

Natural 

Natural 

Gas,  8.65 

Gas,  o 

Producer 

Per  Cent. 

Per  Cent. 

Gas 

Air 

Air 

Carbon  dioxide    . 

C02 

.40 

•  45 

5-7 

Carbon  monoxide 

CO 

1.70 

1.85 

22. 

Oxygen  .... 

0 

I.  80 

.0 

•  4 

Ethylene      .     .     . 
Ethane    .... 
Methane      .     .     . 

C2H4 
C8H6 
CH4 

1.40 

12.95 
68.85 

1.55 
14.20 
75-35 

.6 

.0 

2.6 

Hydrogen    .     .     . 
Nitrogen      .     .     . 

H 

N 

12.90 

6.60 

10.5 
58.2 

Calorific  value  in 

B.T.U.percu.ft. 

1,000+ 

I,IOO+ 

I4olt 

The  above  analyses  are  of  course  by  volume, 
the  first  analysis  of  natural  gas  being  taken  from 
normal  line  gas,  the  8.65  per  cent,  of  air  being 
due  merely  to  leakage  into  the  main,  while  the 
second  analysis  of  natural  gas  is  with  the  air  cal- 
culated out. 

ARTIFICIAL    GAS 

Artificial  gas  has  been  used  in  the  form  of 
producer  gas,  coal  gas  and  water  gas,  but  of 
these  the  only  one  of  importance  in  Open 
Hearth  is  producer  gas. 


A   STUDY    OF   THE    OPEN   HEARTH 

A  modern  producer  consists  essentially  of  a 
vertical  steel  cylinder  of  from  8  to  12  feet  in 
diameter  and  10  to  15  feet  in  height,  this  lined 
with  fire  brick.  At  the  bottom  is  a  grate  on 
which  is  supported  the  mass  of  fuel  about  6  to  7 
feet  in  depth.  From  the  top  of  this  producer 
a  duct  leads  to  the  main  gas  flue  and  at  the 
base  are  openings  for  the  admission  of  steam 
and  air  blast.  There  are  many  different  types 
of  gas  producers,  each  having  certain  points  of 
superiority,  but  our  description  has  to  do  only 
with  the  general  type. 

The  bed  of  coal  being  ignited,  a  blast  of  air 
mixed  with  a  slight  volume  of  steam  is  intro- 
duced. The  carbon  of  the  coal  brought  in  contact 
with  the  air  is  burned  to  CO 2  (carbon  dioxide), 
the  major  portion  of  which  in  turn  passing 
up  through  the  bed  of  hot  fuel,  is  broken  down 
into  carbon  monoxide  (CO).  A  portion  of  the 
steam  which  is  introduced  at  the  same  time  is 
also  decomposed  in  contact  with  the  incandescent 
carbon  forming  hydrogen  and  oxygen,  the  latter 
then  forming  with  the  carbon,  carbon  monoxide. 
In  addition  to  the  above  there  is  distilled  off  a  cer- 
tain amount  of  the  more  volatile  hydro  carbons 
from  the  upper  portions  of  the  coal  bed.  These 
reactions  are  very  simply  expressed  as  follows : 

i st.     Carbon  burned  to  carbon  dioxide. 

C+20=C02. 

2d.      Reduction  of  carbon  dioxide  by  hot 
coal. 

CO2+C=2CO. 

45 


A    STUDY    OF    THE    OPEN    HEARTH 

3d.      Incandescent  carbon  decomposing 
water   and    combining   with 
oxygen. 
C+H2O=CO+2H. 

The  steam,  although  broken  up  and  forming 
hydrogen  and  carbon  monoxide,  both  of  fuel 
value,  does  not  actually  add  to  the  calorific  effi- 
ciency of  the  producer  inasmuch  as  the  reaction 
requires  a  greater  expenditure  of  heat  for  its 
accomplishment  than  is  available  when  the  gases 
formed  by  its  decomposition  are  burned,  but  it 
serves  the  purpose  of  keeping  the  fire  at  a  low 
enough  temperature  to  reduce  the  clinkering, 
and  aids  in  the  operation  of  the  producer.  There 
are  of  course  a  number  of  complicated  secondary 
reactions  which  may  occur  in  addition  to 
the  above,  but  it  is  unnecessary  here  to  go  into 
these. 

It  is  very  necessary  to  stir  the  fire  at  in- 
tervals of  a  few  minutes,  in  order  to  avoid  the 
'forming  of  passages  in  the  coal  bed,  through 
which  the  COa  gas  may  pass  without  being  kept 
in  contact  with  the  hot  bed  of  fuel,  and  thus 
broken  down  into  CO.  Gases  will  of  course 
take  the  path  of  least  resistance,  and  if  the  bed 
is  insufficiently  stirred,  either  by  hand  or  mechan- 
ical stoker,  the  analysis  will  immediately  show 
undue  percentage  of  CO3  in  the  flues.  It  should 
approximate  4  to  6  per  cent. 

By  reference  to  the  previous  table  of  anal- 
yses, the  reason  for  the  comparatively  low 
calorific  value  of  producer  gas  is  apparent  in  the 

46 


A        STUDY        OF        THE         OPEN         HEARTH 

large  proportion  of  nitrogen,  this  unavoidable 
on  the  introduction  of  air.  Nitrogen  is  inert, 
and  its  effect  is  merely  to  dilute  the  gas,  the 
major  portion  of  the  fuel  value  of  producer  gas 
being  in  its  content  of  carbon  monoxide. 

In  what  is  known  as  a  water-sealed  producer, 
the  producer  itself  rests  in  a  pan  containing 
water,  into  which  the  ashes  drop,  and,  being 
water-sealed,  may  be  cleaned  and  the  fires 
attended  to  without  interfering  with  the  opera- 
tion of  the  producer. 

The  bed  of  fuel,  in  order  for  the  best  opera- 
tion of  the  furnace,  must  be  maintained  at  ap- 
proximately 6  feet  in  depth,  this  depth  being 
kept  fairly  constant  by  fresh  charges  of  coal 
introduced  either  by  hand  or  by  a  mechanical 
filling  device. 

FUEL    FOR    MAKING    PRODUCER    GAS 

Although  a  number  of  different  fuels  have 
been  used,  such  as  anthracite  coal,  coke,  peat, 
etc.,  bituminous  coal  is  the  only  one  necessary  to 
consider  here.  The  coal  should  be  an  ordinary 
good  gas  coal.  The  major  portion  of  bituminous 
coals  are  satisfactory  for  use,  provided  they  do 
not  run  too  high  in  sulphur,  preferably  not  over 
i  per  cent.,  although  the  allowable  proportion  of 
sulphur  depends  upon  the  form  in  which  it  is  in 
the  coal.  If  in  such  a  state  as  to  be  very  readily 
volatilized  and  pass  over  with  the  gases,  a  very 
small  portion  may  be  beyond  allowable  limits,  as 
this  is  then  very  rapidly  absorbed  by  the  steel, 


A    STUDY    OF    THE    OPEN    HEARTH 

but  if  in  such  form  as  to  readily  oxidize,  remain- 
ing with  the  ash,  it  may  be  higher.  Lime  is  some- 
times added  to  the  coal  with  the/  idea  of  keeping 
down  the  sulphur  in  the  gas  by  formation  of  a 
sulphate.  The  coal  should  have  a  comparatively 
low  percentage  of  ash.  Other  things  being  equal, 
the  higher  the  percentage  of  volatile  matter,  the 
richer  the  gas  produced,  on  account  of  the  greater 
proportion  of  hydro-carbons.  A  gas  showing 
ample  calorific  efficiency  can  be  manufactured 
from  anthracite  coal,  but  in  actual  operation 
it  would  be  exceedingly  unsatisfactory.  This  is 
due  to  the  lack  of  hydro-carbons  carried  over  in 
the  bituminous  coal  producer,  which  in  the  Open 
Hearth  become  incandescent,  and  by  their  radi- 
ated heat  greatly  increase  the  fuel  value  of  the 
gas  as  compared  with  anthracite  gas  showing 
about  the  same  theoretical  calorific  efficiency. 


In  a  number  of  Open  Hearth  plants,  oil 
vaporized  by  steam  or  air,  is  used  as  a  fuel,  it 
requiring  of  course  no  previous  heating.  The 
fuel  is  of  high  heat-producing  value,  very  easy 
and  simple  to  operate,  and  requires  a  compara- 
tively small  expenditure  for  an  outfit.  Moreover, 
the  fuel  is  regular  in  quality  and  the  furnace  can 
be  operated  very  uniformly.  However,  with  oil 
the  flame  tends  to  be  extremely  sharp  and  cut- 
ting, and  unless  proper  care  is  exercised  it  is  an 
easy  matter  to  burn  out  a  roof  or  cause  over- 
oxidization  of  the  metal  before  the  trouble  is 

48 


A    STUDY    OF    THE    OPEN    HEARTH 

discovered.  In  other  words,  the  flame  is  too 
intense  and  the  heat  rather  too  much  localized  to 
be  by  any  means  ideal.  Nevertheless,  for  reasons 
cited  above,  this  system  possesses  a  number  of 
advantages  where  the  supply  of  oil  is  cheap,  its 
relative  economy  depending  upon  the  relative 
cost  of  coal  and  oil  at  the  plant  considered,  and 
its  selection  is  a  matter  determined  usually  by 
local  considerations. 


49 


A   STUDY    OF   THE    OPEN    HEARTH 

CHAPTER    III 
ACID    OPEN    HEARTH    PROCESS 

The  difference  between  the  acid  and  the  basic 
Open  Hearth  process  results  in  this : 

That  the  acid  process  removes  or  reduces  to 
within  allowable  limits — (i)  carbon;  (2)  silicon; 
(3)  manganese. 

The  basic  process  removes  or  reduces  to 
within  allowable  limits — (i)  carbon;  (2)  silicon; 
(3)  manganese;  (4)  sulphur;  (5)  phosphorous. 

CHARGE 

Since  by  the  acid  process  no  sulphur  or  phos- 
phorous is  eliminated,  the  furnace  charge  must 
be  not  only  of  no  higher  average  percentage  in 
these  impurities  than  is  allowable  in  the  finished 
material,  but  somewhat  lower.  If,  say  there  is 
an  average  percentage  of  .04  per  cent,  in  sulphur 
and  .06  per  cent,  in  phosphorous  in  the  charge, 
it  would  naturally  be  somewhat  higher  than  this 
in  the  finished  steel,  due  to  the  elimination 
of  the  remaining  impurities. 

The  charge  is  generally  made  up  of  scrap  and 
pig  iron,  in  this  country  with  usually  a  consid- 
erably larger  proportion  of  scrap  than  abroad, 
where  the  supply  of  the  latter  is  often  limited,  a 
rough  average  being,  say  25  per  cent,  scrap  and 
75  per  cent,  pig  iron,  while  in  this  country  the 
more  usual  average  will  run  50  to  75  per  cent, 
scrap  and  the  balance  pig,  exact  proportions 
dependent,  however,  upon  the  relative  availa- 
bility of  the  pig  and  scrap  and  their  cost. 

50 


STUDY   OF   THE    OPEN    HEARTH 


Pig  iron  runs  usually  between  3.25  per  cent. 
in  carbon  as  a  minimum,  to  4.25  per  cent,  as 
a  maximum,  the  silicon  varying  rather  widely 
from  as  low  as  i  per  cent,  or  even  under,  up  to 
2.5  per  cent,  or  over,  and  the  manganese  usually 
under  i  per  cent,  with  sulphur  not  over  .05  per 
cent,  and  phosphorous  not  over  .  10  per  cent.  The 
above  of  course  refers  to  pig  iron  suitable  for 
acid  practice. 

The  scrap  varies  from  crop  ends  of  rails, 
structural  shapes,  billets  and  other  heavy  scrap 
to  the  lightest  plate  shearings,  punchings,  bor- 
ings, turnings,  etc.  The  following  are  fairly 
representative  analyses,  showing  the  impurities 
concerned  in  samples  of  pig  and  scrap: 


Elements 

Pig  Iron 

Structural 
Steel  Scrap 

Rail 
Steel  Scrap 

Carbon      .... 

3.00  to  4.00 

.20 

•  45 

Silicon       .... 

1.  00  to  2.00 

.01 

•  15 

Manganese    .  .  ;     . 
Phosphorous      .  .  . 

Under  i.oo 
.10 

.50 
.04 

.90 

.10 

Sulphur     .     . 

.05 

.04 

.075 

PROPORTIONING    THE    CHARGE 

The  exact  proportions  of  each  in  the  charge 
are  dependent  on  the  quality  and  quantity  of 
scrap  obtainable,  as  well  as  the  analysis  of  the 
pig  iron,  particularly  its  silicon  content.  The 
charge  may  be  entirely  of  pig,  provided  a  very 
low  silicon  pig  be  obtained ;  a  certain  proportion 
of  pig,  however,  is  absolutely  essential  to  prevent 
the  comparatively  pure  scrap  from  oxidization. 


A    STUDY    OF    THE    OPEN    HEARTH 

A  large  proportion  of  high  silicon  pig  iron 
and  a  small  amount  of  scrap  would  give  a  large 
volume  of  slag,  so  much  indeed  as  to  seriously 
interfere  with  the  working  of  the  bath,  forming 
such  a  heavy  covering  over  the  metal  as  to  make 
it  difficult  to  thoroughly  penetrate  the  bath 
with  the  heat,  the  operation  would  be  unduly 
prolonged,  the  slag  tend  to  be  highly  viscous 
and  pour  with  difficulty. 

On  the  other  hand,  with  too  large  a  propor- 
tion of  scrap,  so  small  would  be  the  amount  of 
slag  that  the  molten  metal  would  have  very  little 
protecting  envelop,  there  being,  consequently, 
high  losses  from  oxidization,  and  the  charge 
when  melted  so  low  in  silicon,  manganese  and 
carbon  as  to  be  viscid  and  difficult  to  work. 

In  order  to  proportion  the  charge  there  must 
first  be  considered  at  least  the  primary  reactions 
which  occur  in  the  removal  of  the  three  impur- 
ities which  we  are  alone  considering  in  acid 
practice,  i.  e.,  carbon,  silicon  and  manganese,  in- 
asmuch as  sulphur  and  pJwsphorous  are  sup- 
posedly within  allowable  limits. 

The  process  is  throughout  one  of  oxidization, 
the  carbon  being  oxidized  to  carbon  monoxide, 
which  in  turn  further  oxidizes  to  carbon  di- 
oxide, passing  off  as  a  gas — the  silicon  and 
manganese  being  oxidized  and  forming  with  the 
manganese  and  iron  from  the  bath  a  double  sili- 
cate of  manganese  and  iron,  this  rising  to  the  top 
of  the  bath  and  forming  a  slag. 

These  simple  reactions  are  expressed  as  fol- 
lows, together  with  the  atomic  weights  showing 

52 


A    STUDY    OF    THE    OPEN    HEARTH 

the  proportions  by  weight  involved  in  these 
combinations: 

C+O=CO  Si+2O=SiO3  Mn+O=MnO 
12  16  28  28  32  60  55  16  71 
In  other  words,  for  the  oxidization  or  burning 
of  one  atom  of  carbon  there  is  required  one  atom 
of  oxygen,  but  expressed  by  weight  there  will 
be  required,  because  of  the  difference  in  their 
atomic  weights,  1.333  parts  of  oxygen;  in  the 
same  way  one  atom  of  silicon  will  require,  by 
weight,  1.143  parts  of  oxygen;  one  atom  of  man- 
ganese will  require,  by  weight,  .291  parts  of 
oxygen.  Merely  expressing  this  in  terms  of 
oxygen : 

One  part  of  oxygen  oxidizes  .750  parts  of 
carbon,  or  .875  parts  of  silicon,  or  3.438  parts  of 
manganese. 

Now,  since  one  part  of  carbon  requires  1.333 
parts  oxygen,  and  one  part  silicon  1.143  parts 
oxygen,  one  part  of  silicon  is  equivalent  to 

-^=.857  carbon,  i.  e.,  so  far  as  the  amount  of 

oxygen  with  which  it  will  combine  is  concerned. 
In  the  same  way  one  part  of  manganese =.218 
parts  carbon. 

In  figuring  the  charge,  assume  that  a  pig  and 
a  scrap  with  the  following  fairly  representative 
analyses  are  concerned: 

Elements  Pig  Scrap 

Carbon          .         .         .         3.5$  .20% 

Silicon  .          .          .        1.50$  .01$ 

Manganese  .         .         .         .70$  .50$ 

53 


A    STUDY    OF    THE    OPEN    HEARTH 

Expressing  all  these  impurities  in  terms  of 
carbon,  there  is  in  the 

Pig  Iron 

3.5$    carbon  =3.500$  carbon 

1.5$    silicon  x-^57  =  1.285$  carbon 

.70$  manganese  x.2i8  =    -153$  carbon 

Total  .         .        4.938$  carbon 
Scrap 

.20$  carbon  =     .20$    carbon 

.01$  silicon  ^.857  =     .008$  carbon 

.50$  manganese  x.2i8  =     .109$  carbon 

Total         .         .          .317$  carbon 

In  other  words,  we  are  dealing  with  a  pig  and 
scrap  which  require  for  the  oxidization  of  their 
impurities  the  same  amount  of  oxygen  as  though 
the  pig  had  4.938  per  cent,  carbon  and  no  other 
impurities;  the  scrap  .317  per  cent,  carbon  and 
no  other  impurities. 

The  elimination  of  the  impurities  is  effected 
in  two  distinct  stages,  i.  e.,  during  the  melting 
of  the  bath  by  the  oxygen  of  the  flame,  and  after 
the  melting  when  this  is  augmented  by  the  action 
of  the  oxides  of  iron  formed  during  melting  and 
added  after  melting. 

For  purposes  of  figuring  the  charge,  assume 
what  is  a  fair  average,  say  40  per  cent,  of  the 
impurities  to  be  oxidized  during  the  melting  (the 
influences  governing  this  percentage  will  be  taken 
up  later  under  "Elimination  of  Impurities"). 
Assume  also  that  a  soft  steel  heat  is  being  made, 
to  be  tapped  at  about  .20  carbon.  It  should  have 
when  melted  approximately  .60  carbon.  The 

54 


A   STUDY   OF   THE    OPEN    HEARTH 

problem  now  is,  merely  having"  a  pig  of  total 
impurities,  figured  in  terms  of  carbon  of  4.938 
per  cent,  and  scrap  .317  per  cent.,  what  pro- 
portion of  the  two  will  give  an  average  of  .  60  per 
cent,  when  40  per  cent,  of  this  total  carbon  has 
been  already  oxidized? 

Obviously,   .60  =  ioof° —  40$  =  60$  or 
.60 

—  X    IOO    —    1. 00 

60 

which  represents  the  total  impurities  (expressed 
in  carbon)  in  the  charge  before  melting,  this 
total  to  be  the  average  from  the  above  pig  and 
scrap. 

Expressing  it  in  per  hundred  parts  or   per 
cent. — : 

Let  X  —  number  parts  of  pig. 
loo  —  X  =  number  parts  of  scrap. 

Then 

4.938  X  =  total   impurities   in    pig    (ex- 
pressed in  terms  of  carbon). 
.317   (loo-X)   —  total  imptirities  in  scrap  (ex- 
pressed in  terms  of  carbon). 
Therefore, 

4.938  X  +  .317  (loo-X)  =  100.0 

X    =  i  $t  pig. 
loo  —  15  =  85$  scrap. 


METHOD    OF    CHARGING 


Although  authorities  differ  as  to  the  order  in 
which  the  material  is  to  be  charged,  it  is  almost 
the  universal  practice  to  charge  the  pig  iron  first 


55 


A    STUDY    OF   THE    OPEN    HEARTH 

and  on  it  the  scrap.  Some  charge  a  portion  of 
the  pig  iron,  then  the  scrap,  following  with  the 
remainder  of  the  pig. 

The  pig  is  -usually,  however,  placed  on  the 
bottom  to  protect  the  latter  from  the  oxide  of 
iron  formed  by  oxidization  of  the  scrap  by 
the  flame.  This  oxide  in  coming  into  contact 
with  the  sand  bottom  forms  a  silicate  of  iron, 
very  rapidly  scorifying  and  cutting  it  away. 

Campbell  advises  charging  the  scrap,  then  the 
pig,  stating  that  the  pig  melting  and  trickling 
down  over  the  scrap  protects  it  from  oxidization, 
the  oxygen  of  the  flame  having  a  greater  affinity 
for  the  carbon,  silicon  and  manganese  of  the  pig 
than  for  the  metal  itself.  However,  this  is  by 
no  means  the  usual  practice. 

With  very  heavy  scrap  there  is  possibly  no 
great  advantage  in  one  method  over  the  other, 
as  there  is  under  such  conditions  comparatively 
little  oxidization  but  with  very  light  scrap,  such 
as  light  plate  shearings,  it  is  important,  for 
not  only  is  the  bottom  rapidly  scoured  away 
by  contact  with  the  oxide  of  iron,  but  a  hole  may 
very  possibly  be  eaten  almost  entirely  through, 
and  the  surrounding  portion  of  the  bottom  become 
so  impregnated  with  iron  as  to  greatly  reduce 
its  refractoriness.  This  scorification  continues 
until  the  slag  formed  becomes  either  neutral  or 
acid  throughout,  combining  with  the  silica. 

ELIMINATION    OF    IMPURITIES 
MELTING 

In  the  manufacture  of  soft  steel  the  charge  is 
often  so  proportioned  that  practically  all  the 

56 


A    STUDY    OF    THE    OPEN    HEARTH 

silicon  is  oxidized  by  the  time  the  charge  is 
melted  and  the  carbon  is  then  reduced  to  from 
.60  to  .80  per  cent.,  this  percentage  of  carbon 
later  being-  reduced  by  the  addition  of  ore. 

In  order  that  the  flame  at  the  beginning  of 
melting  may  oxidize  the  scrap  as  little  as  possible, 
there  is  sometimes  admitted  only  an  insufficient 
supply  of  air,  this  keeping  the  flame  smoky.  It 
is,  however,  in  a  measure  self-regulating,  as  the 
flame  striking  the  cold  stock,  the  gases  are  chilled 
and  a  portion  of  the  carbon  precipitated.  Many 
Open  Hearth  men,  however,  believe  that  the  best 
results  are  secured  in  getting  the  stock  melted 
down  at  the  earliest  possible  minute,  even  at  the 
expense  of  slightly  greater  oxidization. 

ELIMINATION     DURING    MELTING 

The  amount  of  oxidization  during  melting  is 
much  influenced  by  the  character  of  the  flame,  a 
sharp  flame  increasing  the  action ;  by  the  presence 
of  hydrogen,  which  has  the  same  effect,  and  by  the 
port  construction,  if  the  ports  are  so  inclined  that 
the  air  is  allowed  to  play  directly  upon  the  metal. 
This  latter  has  a  marked  tendency  toward  increas- 
ing oxidization. 

It  is  also  apparent  that  the  percentage  of 
oxidization  will  be  in  a  great  measure  dependent 
on  the  analysis  of  the  pig  iron  as  well  as  the  pro- 
portions of  pig  and  scrap,  whether  light  or  heavy, 
as  well  as  the  way  in  which  it  is  charged.  The 
general  working  of  the  furnace  as  well  has  also  an 
important  bearing. 

57 


STUDY        OF        THE         OPEN         HEARTH 


In  what  may  be  termed  a  normal  heat,  for 
instance  for  soft  steel,  and  with  the  furnace 
tinder  normal  working  conditions,  the  elimination 
of  the  manganese,  silicon  and  carbon-  occurs  in 
the  order  named  and  in  accordance  with  their 
relative  affinity  for  oxygen  (see  the  combining 
weights  under  "Proportioning  Charge")  and  in 
American  practice,  i.  e. ,  with  the  scrap  and  pig 
here  obtainable,  practically  all  the  manganese  and 
silicon  are  oxidized  during  melting,  leaving  only 
say  .60  per  cent,  carbon  in  the  bath. 

The  following  table,  taken  from  Campbell, 
shows  the  average  elimination  in  two  series  of 
heats,  Group  I  of  nineteen  heats  on  producer 
gas;  Group  II  of  six  heats  with  oil  vapor. 

ELIMINATION    OF   METALLOIDS  IN    AN   OPEN    HEARTH 
CHARGE 


Nature  of  Sample 

Group  I 

Group  II 

Pig  iron,  pounds       .     .     . 

11,700 

20,700 

Steel  scrap,  pounds 

45,550 

36,800 

Composition    of    original 

(Si 

.40 

•  65 

charge,  per  cent,  (esti- 

\ Mn 

.90 

.85 

mated)     

(G 

1  .00 

1.50 

Metal  when  melted,   per 
cent.    .              .... 

(Si 
\  Mn 

.02 
.09 

.05 
.06 

(c 

•  54 

.64 

Slag  after  melting,  per  j 
cent  1 

Si02 
MnO 
FeO 

50.24 
21.67 
23.91 

49.46 
13.16 
33-27 

In  English  practice  where  much  larger  pro- 
portions of  pig  are  used,  this  pig  running  much 

58 


A    STUDY    OF    THE    OPEN    HEARTH 

higher  in  silicon,  only  from  35  to  50  per  cent,  of 
the  silicon  will  be  removed  during  melting,  and 
possibly  30  per  cent,  carbon,  although  nearly  all 
the  manganese  will  be  oxidized. 

In  cases  where  a  very  light  scrap  is  used,  with 
a  considerable  formation  of  iron  oxide,  this  may 
react  locally  to  decarburize  the  adjacent  portion 
of  the  bath  before  the  whole  is  melted,  but  this 
action  is  not  usually  on  so  large  a  scale  as  to  be 
important. 

ELIMINATION    AFTER    MELTING 

There  now  remains  in  the  bath,  say  .60  carbon 
(considering  the  soft  steel  heat)  which  must  be 
further  oxidized  and  dependent  on  conditions 
previously  covered,  there  may  be  as  well  certain 
amounts  of  manganese  and  silicon.  This  carbon 
together  with  the  remainder  of  silicon  and  man- 
ganese, if  any,  is  oxidized  by  keeping  the  bath  at 
a  good  heat  and  introducing  from  time  to  time 
iron  ore,  a  red  oxide,  hematite,  sometimes 
termed  "vermillion"  ore,  being  the  best,  this 
ore  approximating  60  per  cent,  in  iron,  4  to  4^ 
per  cent,  in  silicon,  and  possibly  .  1 1  in  phosphor- 
ous, with  manganese  running  .6  per  cent.,  lime 
1.6  and  with  only  a  trace  of  sulphur. 

It  is  essential  that  the  ore  be  as  free  as  possible 
from  impurities,  and  as  the  oxygen  is  the  active 
agent,  the  higher  the  ore  is  in  oxide  of  iron  the 
more  efficient  it  is.  In  order  that  it  may  pene- 
trate the  slag,  reaching  the  metal  where  its  work 
is  to  be  done,  it  should  be  of  high  specific  gravity 
and  in  comparatively  large  lumps.  Otherwise, 

59 


A   STUDY   OF    THE    OPEN    HEARTH 

if  in  fine  form,  portions  will  become  entangled 
in  the  more  or  less  viscous  slag. 

The  oxidization  is  effected  in  the  following 
reactions : 

Carbon:  Re2O3  +     $C  =     3  CO  +  2Fe 

Silicon:          2Fe2O3  +    aSi  =  3  SiO2  +  4?e 
Manganese :   Fe2O3  +  3Mn  =  3  MnO  +  2Fe 

The  CO  gas  escaping  as  oxidization  proceeds, 
produces  a  bubbling  or  boil  over  the  entire  sur- 
face of  the  bath,  qxposes  the  metal  to  the  flame, 
and  by  its  combustion  serves  to  maintain  the 
high  temperature.  If  there  is  any  silicon  and 
manganese  in  the  bath,  due  to  the  greater  affinity 
for  oxygen,  they  will  be  first  oxidized,  and  when 
such  oxidization  is  complete,  carbon  will  follow. 

The  ore  is  added  in  small  quantities  from  time 
to  time  as  needed  in  the  judgment  of  the  melter, 
dependent  not  only  on  the  quantity  of  impurities 
in  the  bath,  but  on  the  condition  of  the  bath  and 
slag,  whether  hot  or  cold,  and  the  general  work- 
ing conditions  of  the  furnace.  If  hot,  the  ore 
can  be  added  much  faster  than  if  cold,  when  any 
large  quantity  will  chill  the  bath.  Furthermore, 
with  a  bath  of  high  carbon,  the  ore  does  not 
appear  to  react  as  rapidly  as  when  the  carbon  is 
reduced  to  a  lower  percentage,  the  general  char- 
acter of  the  slag  also  influences  the  rapidity  of 
oxidization  materially. 

Although  it  is  a  simple  matter  from  the  equa- 
tions involved  in  these  reactions  to  calculate  the 
amount  of  ore  necessary  to  oxidize  any  amount 

60 


STUDY        OF 


HEARTH 


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61 


A    STUDY    OF    THE    OPEN    HEARTH 

of  impurities  in  the  bath,  the  conditions  con- 
sidered have  such  an  important  effect  as  to 
render  any  such  calculations  absolutely  useless, 
and  in  actual  practice  it  is  never  relied  upon.  As 
of  interest,  however,  the  table  on  the  preceding 
page  is  given,  taken  from  Campbell's  article  in 
the  "Transactions  of  the  American  Institute 
of  Mining  Engineers." 

A  study  of  this  table  will  bear  out  the  state- 
ments already  made  as  to  the  quantities  of 
ore  required,  due  to  conditions  of  stock,  gas, 
furnace,  operation,  slag,  etc.,  and  apparently 
almost  wholly  independent  of  the  amount  of  im- 
purities to  be  oxidized.  To  make  a  general  state- 
ment, one  authority  mentions  that  approximately 
250  pounds  of  ore  in  a  normal  heat  will  oxidize 
carbon .  i  per  cent. ,  but  this  statement  is  to  be  con- 
sidered only  as  approximate  and  dependent  on  the 
conditions  as  cited  above.  It  is  apparent  from  the 
equations  showing  the  reactions  on  introduction 
of  the  ore  that  a  considerable  amount  of  the  metal 
will  be  by  this  reduction  added  to  the  bath. 

After  the  impurities  have  been  sufficiently 
oxidized  by  the  ore  additions,  the  bath  is  ready 
for  recarburizing  or  recarbonizing  as  it  is  some- 
times termed. 

SLAG 

The  slag  formed  from  the  oxidization  of  the 
impurities  in  the  pig  and  scrap,  the  sand  attached 
to  the  pig  together  with  the  impurities  in  the 
ore,  and  whatever  oxide  of  iron  may  have  been 

62 


A   STUDY   OF   THE    OPEN    HEARTH 

taken  from  the  bath,  serves  as  a  covering  to  pro- 
tect the  metal  from  oxidization,  also  to  transmit 
the  heat  and  oxygen  to  the  bath.  Its  office  is  an 
important  one,  and  its  control  has  a  very  marked 
bearing  on  the  proper  working  of  the  heat. 

Of  course,  with  a  high  silicon  pig  in  large 
proportions  there  is  bound  to  be  a  much  heavier 
slag  than  with  a  low  silicon  pig,  thus  with  a  large 
proportion  of  scrap  and  low  silicon  pig  the  slag  may 
be  so  light  as  to  afford  scanty  protection  to  the 
metal.  It  is  important  that  the  slag  be  fluid, 
neither  pasty  nor,  on  the  other  hand,  too  thin. 
Especial  care  is  required  in  this  at  time  of  tap- 
ping. If  too  viscous,  the  addition  of  a  few  lumps 
of  lime  may  remedy  the  matter ;  if  too  thin,  it  is 
an  indication  of  a  slag  too  rich  in  oxides  of  iron 
and  manganese,  and  one  liable  to  produce  wild 
metal.  The  determination  of  a  good  tapping 
slag  is  necessarily  possible  only  from  experience. 

The  acid  slag  will  usually  run  somewhat  under 
10  per  cent,  of  the  total  weight  of  the  charge. 
The  table  on  the  following  page  from  Campbell's 
article  already  referred  to,  shows  the  history  of 
metal  and  slag  in  19  and  6  heats  respectively 
on  an  acid  furnace. 

From  this  it  will  be  seen  that  the  percentage 
of  silica  is  practically  constant  from  the  time  of 
melting  to  tapping,  running  closely  around  50 
per  cent.,  and  that  although  the  MnO  was  less  in 
Group  II,  the  FeO  increased,  the  sum  of  the  two 
remaining  practically  constant.  The  slag  is 
within  certain  limits  almost  self -regulating,  i.  e. , 

63 


STUDY    OF    THE    OPEN    HEARTH 


if  there  is  an  insufficient  quantity  of  the  basic 
MnO  and  FeO  to  satisfy  the  silica,  the  deficiency 
will  be  made  up  by  abstracting  the  iron  from  the 
bath.  On  the  other  hand,  if  too  low  in  silica  to 
satisfy  the  bases,  the  balance  will  be  restored  by 
silica  taken  from  the  furnace  bottom.  Either  is 
objectionable,  the  one  robbing  the  melt,  the 
other  scorifying  the  bottom.  With  a  good  work- 
ing slag,  i.  e. ,  with  sufficient  oxides  to  satisfy  this 
silica,  and  vice  versa,  any  ore  additions  have 
practically  no  effect  on  the  iron  content  of  the 
slag,  as  the  iron  is  merely  reduced  and  absorbed 
by  the  bath. 


Composition,  Per  Cent. 


Subject 

Group  I 
19  Heats,  Soft  Coal 
Gas 

Group  II 
6  Heats,  Oil 
Gas 

After 
Melting 

End  of 
Operation 

After 
Melting 

End  of 
Operation 

fSi        .      .      . 
Metal  \  Mn    .     .     . 

.02 
.09 

•  54 

.02 
.04 
•13 

.05 
.06 
.64 

.OI 
.02 
.  12 

Slag 

rsio8.    .   . 

MnO      .     . 
1  FeO  .     .     . 
[  MnO  +  FeO 

50.24 
21.67 
23.91 

45.58 

49.40 
16.50 
29.79 
46.29 

49.46 
13.16 

33-27 
46.43 

49-36 
11.30 
34.ii 
45.41 

64 


A    STUDY    OF    THE    OPEN    HEARTH 

CHAPTER  IV 

RECARBURIZATION 

This  term  is  somewhat  of  a  misnomer  inas- 
much as  the  addition  of  carbon,  to  bring  the  heat 
to  a  proper  percentage,  is  only  one  of  the  objects 
which  may  be  summed  up  as  follows  : 

(a)  Removal  or  neutralization  of   gases   and 
oxides  retained  in  the  heat. 

After  a  heat  is  finished,  with  the  exception  of 
adding  the  recarburizer  there  is  found  to  be  in 
the  metal  when  tapped,  certain  oxides  of  iron  or 
other  metals  as  well  as  gases,  such  as  oxygen, 
hydrogen,  nitrogen  and  carbon  monoxide. 
These  if  not  removed  or  neutralized,  serve  to 
render  the  metal  wild,  in  other  words,  froth  and 
bubble  in  the  ladle  and  moulds  and  prevent  a 
good  sound  ingot  or  casting. 

(b)  Introduction  of  metals. 

For  an  acid  Open  Hearth  structural  steel,  the 
specification  will  call  for,  say  50  manganese,  but 
the  entire  manganese  content  in  the  pig  and  scrap, 
as  has  been  covered,  has  of  course  been  oxidized 
in  the  process  of  manufacture  and  manganese 
must  consequently  now  be  added. 

Also  certain  steel  castings  and  special  steels 
may  require  very  high  silicon  content,  this 
introduced  by  the  addition  of  certain  alloys  high 
in  silica,  such  as  silicon  carbide,  and  in  the  manu- 
facture of  chrome  and  nickel  steels  there  are 
introduced  alloys  of  nickel  and  chromium. 


A    STUDY    OF    THE    OPEN    HEARTH 

Aluminum  is  also  added  in  small  quantities  to 
quiet  the  metal  in  the  ladle  and  secure  sounder 
ingots.  It  also  promotes  fluidity  of  the  metal. 

(c)   Regulation  of  carbon  content. 

RECARBURIZERS 

Although  in  making  structural  or  soft  steel, 
such  as  has  been  previously  considered,  ferro- 
manganese  is  almost  the  only  recarburizer  used, 
there  are  several  others  such  as  speigeleisen,  ferro- 
silicon,  silico  speigel  and  silicon  carbide,  the  latter 
sometimes  employed  in  the  manufacture  of  high 
carbon  and  special  steels.  Ferro-manganese  is 
an  alloy  of  manganese,  carbon  and  iron,  standard 
ferro-manganese  running  close  to  80  per  cent, 
manganese.  Speigeleisen  is  identical  with  ferro 
save  that  its  manganese  shows  under  20  per  cent. 
Ferro-silicon  is  merely  a  very  high  silicon  pig 
iron.  Silico  speigel  is  really  a  combination  of 
the  latter  two,  having  the  high  manganese  of  the 
former  and  the  high  silicon  of  the  latter.  All  the 
above  are  made  in  the  blast  furnace,  but  only  of 
course  on  special  burdens.  Silicon  carbide  is 
the  product  of  the  electrical  furnace. 

In  addition  to  the  above,  pig  metal  is  em- 
ployed as  a  recarburizer,  using  the  word  in  the 
strictest  sense,  and  powdered  coal  or  coke,  these 
for  the  purpose  of  effecting  the  carbon  only. 

METHODS     OF    ADDITIONS 

Two  methods  are  available  for  making  these 
additions,  i.  e.,  in  the  furnace  or  in  the  ladle, 

66 


A    STUDY    OF    THE    OPEN    HEARTH 

although  a  combination  of  the  two  is  sometimes 
employed.  Referring  especially  to  paragraphs 
"a"  and  "b,"  ferro-manganese  is  most  widely 
used  in  acid  Open  Hearth  practice,  and  in  addi- 
tion to  furnishing  the  necessary  manganese  con- 
tent, it  also  serves  to  reduce  whatever  oxide  of 
iron  there  may  be  in  the  bath,  as  well  as  to 
remove  the  free  oxygen  that  may  be  held  in  a 
gaseous  form,  the  oxide  of  iron  being  removed  in 
its  reduction  to  metallic  iron,  its  oxygen  going  to 
the  manganese.  Ferro,  as  it  is  often  termed,  is 
often  heated  at  least  to  redness  before  being  in- 
troduced, whether  in  the  furnace  or  ladle,  but 
this  is  hardly  necessary,  as  with  80  per  cent, 
manganese  the  addition  is  comparatively  a  small 
one  and  has  little  actual  effect  in  chilling  either 
the  bath  or  the  metal  in  the  ladle.  This  is  true  in 
heats  of  any  considerable  size,  although  of  course 
if  very  small  heats  are  taken,  such  as  3  to  5  tons 
and  recarburized  in  the  ladle  the  ferro  would  pre- 
ferably be  heated  or  melted  before  adding. 

The  advantage  of  adding  the  ferro- 
manganese  in  the  furnace  rather  than  in  the 
ladle  is  that  it  can  there  rather  better  be 
stirred  and  so  mingle  fully  with  the  bath,  but 
on  the  other  hand,  manganese  being  very  read- 
ily oxidized,  there  is  a  very  considerable  oxid- 
ization in  the  furnace  and  consequent  loss,  as 
the  ferro  is  subjected,  although  only  for  a  short 
space  of  time,  not  only  to  the  effect  of  the  iron 
oxide  and  gases  in  the  metal  but  to  the  action 
of  the  flame  and  slag  as  well,  and  although  but  a 

67 


A    STUDY    OF    THE    OPEN    HEARTH 

minute  or  so  may  be  required  for  the  melting  of 
the  ferro  in  the  bath,  there  is  yet  time  for  losses 
averaging  very  close  to  40  per  cent,  of  the  man- 
ganese so  added.  If  added  in  the  ladle,  on  the 
other  hand,  it  is  apparent  that  such  portion  of  the 
loss  as  is  due  to  the  contained  oxides  of  iron, 
gases,  etc.,  will  be  unchanged,  but  the  man- 
ganese will  not  be  subjected  to  additional  oxidi- 
zation by  flame  and  slag.  If  added  in  the  ladle 
the  loss  will  be  possibly  20  to  30  per  cent. 

In  general,  as  regards  the  losses  of  manganese, 
since  these  losses  are  dependent  not  only  on  the 
oxides  contained  in  the  bath  as  well  as  the  gases, 
but,  wlnen  made  in  the  furnace,  on  the  condition 
of  the  slag,  working  of  the  furnace,  etc.,  it  is 
apparent  that  these  losses  will  be  as  varied  as  are 
the  conditions  controlling  them  and  no  definite 
statement  can  be  made  to  cover  them.  However, 
when  made  in  the  ladle  it  is  obvious  that  they 
will  be  more  regular. 

Assuming  that  we  are  working  with  a  soft  steel 
in  which  the  manganese  has  been  entirely  elim- 
inated in  the  operation  of  the  heat  and  .50  per 
cent,  manganese  is  desired  in  the  charge,  assum- 
ing also,  say  a  40  per  cent,  loss  and  that  we  are 
working  with  an  80  per  cent,  ferro,  the  heat 
being  30,000  pounds: 

30, ooo  x.  $0%  =  150  pounds  manganese. 

Therefore,  since  there  will  be  40  per  cent, 
loss — 

150  pounds  =  (100$  —  40$)  =  60^ 
or  100$  =  250  pounds  manganese. 

68 


A    STUDY    OF    THE    OPEN    HEARTH 

Then  with  an  alloy  of  80  per  cent,  manganese 
there  will  be  required : 

250  pounds  =  80% 
or  100^  =  312.5  pounds  ferro-manganese. 

Additions  of  silicon  where  necessary  either 
for  special  steels  or  in  order  to  raise  the  tempera- 
ture for  very  hot  metal  where  intricate  castings 
must  be  made,  may  be  added  by  any  of  the  above 
mentioned  high  silicon  alloys.  The  losses  either  in 
ladle  or  in  the  furnace  are  somewhat  higher  than 
is  the  case  with  ferro-manganese. 

Aluminum  is  added  in  the  ladle  or  in  the 
mould  in  either  shot  or  ingot  form  from  a  few 
ounces  up  to  several  pounds  per  ton  of  steel, 
dependent  upon  the  class  of  steel,  the  purpose 
for  which  it  is  used,  the  type  of  ingot,  etc.  Inas- 
much as  the  aluminum  serves  to  neutralize  or 
deoxidize  the  oxides  which  are  present  in  the 
metal,  consequently  reducing  the  amount  of 
blow-holes,  it  of  necessity  increases  the  size  of 
pipe  in  the  ingot,  this  pipe  merely  being  the 
shrinkage  cavity.  In  other  words,  it  localizes 
the  shrinkage  and  the  exact  amount  which  it  is 
best  to  use  is  dependent  upon  the  particular 
after-treatment  which  the  ingot  receives. 

Referring  to  **c"  (Regulation  of  Carbon 
Content),  the  exact  method  of  this  regulation  is 
varied  not  only  in  the  manfacture  of  steels  of 
varying  carbons,  but  in  the  same  steels  accord- 
ing to  the  particular  ideas  of  the  melter  and  the 
way  the  furnace  may  be  working.  In  general, 

69 


A   STUDY   OF   THE    OPEN    HEARTH 

in  making  soft  steel  and  using  ferro  as  a  recar- 
burizer,  it  is  apparent  that  the  addition  of  the 
ferro  will  be  so  small  that  its  carbon  content  will 
have  comparatively  little  effect  in  raising  the 
carbon  of  the  heat.  Such  as  it  is,  however,  it 
must  of  course  be  taken  care  of.  In  making 
soft  steel,  for  instance,  it  is  often  customary  to 
boil  it  down  to  say  .08  carbon  and  then  bring 
back  to  the  proper  carbon  for  tapping  by  the 
addition  of  a  pure  pig  metal  charged  on  the 
sides  of  the  hearth  and  allowed  to  run  into  the 
bath,  making  sure  that  this  metal  is  well  melted 
and  stirred  in.  It  may  also  be  added  in  a  molten 
state  in  the  ladle.  Another  method  for  the  addi- 
tion of  carbon  (sometimes  termed  the  Darby 
process)  is  by  the  mixture  of  coal  or  coke  dust  in 
the  ladle,  approximately  40  to  50  per  cent,  of  the 
carbon  so  added  being  taken  up  by  the  metal,  the 
amount  however,  being  dependent  in  a  great 
measure  on  the  temperature,  hot  steel  absorbing 
considerably  more  than  if  poured  at  a  low  tem- 
perature. 

In  the  manufacture  of  hard  or  high  carbon 
steels,  where  the  carbon  is,  say  from  .40  to  i.o 
per  cent,  it  is  usually  the  custom  to  "catch  it 
coming  down,"  /.  e.,  to  stop  the  process  at  the 
proper  point  or  practically  there.  It  is  often 
worked  down  a  little  under  the  desired  carbon  for 
tapping  and  then  brought  back  by  the  addition  of 
a  little  pig  in  the  furnace  or  coal  in  the  ladle.  It 
is  seldom,  however,  that  it  is  attempted  to  add 
all  the  carbon  in  a  heat  to  run  over  .34  or  .40  in 

70 


A    STUDY    OF    THE    OPEN    HEARTH 

the  ladle,  although  this  is  perfectly  possible. 
The  coal  or  coke  when  added  is  in  the  form  of 
dust  weighed  out  in  paper  sacks,  so  that  each 
sack  will  give  a  definite  amount. 

Assume    a   5o-ton  furnace  heat,    tapping  for 
instance    109,000   pounds  in  the  ladle,   and  also 
assuming   that  a  carbon   from  .38  to  .42  in  the 
ingot    is    desired   and   that   the  heat   has   been 
worked  down  to  .10  carbon,  then 
.42  —  .10  =  .32  to  be  added; 
109,000  x  .32  per  cent.  =  348.8 
i.  <?.,  when  tapped  from  the  ladle  the  steel  is  to 
contain  348.8   pounds   more  carbon   than  when 
ready  to  tap  from  the  furnace. 

In  the  best  anthracite  coal  used  for  this  work, 
but  about  44  per  cent,  of  its  weight  is  available 
carbon,  i.  e.,  absorbed  by  the  steel,  the  balance 
being  the  ash,  etc.,  and  the  large  amount  lost  by 
combustion;  therefore, 

348.8  pounds  equal  44  per  cent. 
100  percent,  equals  790  pounds. 

Therefore,  there  would  be  added  in  the  ladle 
approximately  800  pounds  of  the  crushed  coal. 

TAPPING 

The  heat  being  ready  to  tap,  a  bar  is  driven 
through  the  tap  hole  and  this  hole  then  enlarged 
from  the  charging  side  by  means  of  a  long  bar 
until  the  slag  and  metal  flow  freely. 

If  the  hole  is  properly  cleaned  from  slag  and 
metal  at  the  end  of  each  heat,  there  will  be 
little  trouble  from  hard  tap  holes,  but  if  proper 

71 


A    STUDY    OF    THE    OPEN    HEARTH 

precautions  are  not  observed  and  a  portion  of 
slag  and  metal  allowed  to  remain,  this  will  freeze 
and  it  will  be  very  difficult  to  sledge  away,  the 
bar  used  in  drilling  softening  before  much  prog- 
ress can  be  made. 

In  some  instances  sledging  has  been  resorted 
to  ten  to  twenty-five  or  even  thirty-six  hours  be- 
fore successful.  In  cases  of  this  kind  the  fol- 
lowing procedure  has  been  tried  with  marked 
success.  From  the  tapping  side  clean  out  the 
hole  as  much  as  possible,  ram  full  with  powdered 
anthracite  or  coke;  then  stir  the  bath  directly  in 
front  of  the  tap  hole,  making  it  boil,  when  the 
heat  from  the  bath  penetrating  the  frozen  metal 
will  cause  it  to  absorb  from  the  coal  with  which 
the  hole  is  plugged  sufficient  carbon  to  so  lower 
its  melting  point  that  the  hole  will  melt  out  in 
from  one-half  hour  to  an  hour  and  a  half. 
Of  course,  as  furnace  practice  improves  there  is 
less  and  less  trouble  of  this  kind,  but  it  will 
sometimes  occur  when  apparently  every  care  is 
exercised. 

SULPHUR 

Although  the  stock  selected  for  the  heat  may 
be  amply  low  in  sulphur,  yet  there  is  a  possi- 
bility of  such  absorption  from  the  gas  if  a  sul- 
phurous coal  is  used,  and  from  the  ore  if  high  in 
sulphur,  as  to  bring  this  element  beyond  allow- 
able limits.  With  the  same  coal,  however,  vary- 
ing amounts  may  be  absorbed,  as  when  the  fur- 
nace works  cold  the  bath  is  subjected  for  a 

72 


A    STUDY    OF    THE    OPEN    HEARTH 

much  longer  period  to  the  action  of  the  gases, 
and  due  either  to  this  or  the  peculiar  conditions 
attendant  upon  it,  sulphur  is  much  more  read- 
ily absorbed.  The  addition  of  small  amounts  of 
lime  used  with  the  coal  may  tend  to  fix  the 
sulphur  in  the  ash,  but  this  addition,  unless 
made  with  care,  causes  trouble  in  the  producer 
due  to  the  clinkering  of  the  coal. 

SAMPLES    AND    TESTS 

In  general,  in  acid  practice  but  few  samples 
are  usually  necessary  to  follow  the  carbon  in  the 
bath  carefully.  These  samples  are  taken  merely 
by  dipping  a  small  quantity  from  the  molten 
bath  with  a  spoon,  pouring  into  a  mold,  quench- 
ing and  breaking.  From  the  appearance  of  the 
fracture  the  carbon  is  estimated,  a  good  melter 
usually  coming  within  two  or  three  "points" 
or  hundredths  of  i  per  cent,  in  carbon,  about  .20 
or  under.  With  carbon  higher  than  this  there  is 
greater  liability  to  error.  The  first  sample  is 
sometimes  taken  shortly  after  melting,  and  then 
the  melter,  knowing  with  just  what  carbon  he 
has  to  deal,  works  it  down  to  a  point  he  judges 
a  little  above  the  required  carbon  and  takes 
another  sample.  Then  when  the  heat  is  deemed 
ready  to  tap,  a  third  may  be  taken  and  the  frac- 
ture test  checked  up  by  a  rapid  analysis  in  the 
laboratory,  requiring  not  more  than  ten  minutes. 
The  heat,  if  then  satisfactory,  is  tapped. 

The  exact  number  of  tests  on  heats  varies, 
dependent  upon  the  particular  practice  at  the 

73 


A    STUDY    OF    THE    OPEN    HEARTH 

works,  the  way  in  which  the  furnace  is  running, 
etc.,  as  well  as  upon  the  skill  of  the  melter  in 
judging-  his  bath. 

The  temperature  of  the  furnace  and  of  the 
metal  at  its  various  stages  is  also  determined 
largely  by  eye.  Stirring  by  iron  bars  also  gives 
a  very  good  indication  of  the  temperature  of  the 
bath,  both  from  the  "  feel  "  of  the  metal,  whether 
liquid  or  viscous,  and  from  the  way  the  bar  is 
melted  off — if  clean  cut,  a  high  temperature;  if 
rounded,  lower  temperature. 

By  the  color  of  the  slag,  flame  and  interior 
of  the  furnace  the  relative  temperatures  are  also 
judged. 


74 


A    STUDY    OF    THE    OPEN    HEARTH 

CHAPTER  V 

BASIC    OPEN    HEARTH    PROCESS 

As  previously  noted,  the  result  of  the  basic 
process  is  the  removal,  or  reduction  to  within 
allowable  limits,  of  carbon,  silicon,  manganese, 
sulphur  and  phosphorus,  i.  e.,  as  distinguished 
from  the  acid  process,  sulphur  and  phosphorus 
are  in  a  great  measure  under  control.  This 
means  that  stock  not  suitable  for  the  acid 
process  is  still  available  for  the  basic,  and  that 
the  analyses  of  the  steel  will  yet  be  in  all  respects 
satisfactory. 

There  are  in  this  country  vast  bodies  of  low 
phosphorous  ores  yielding  a  pig  iron  too  high  in 
phosphorus  for  the  acid  Open  Hearth,  too  low 
for  the  basic  Bessemer,  but  which  the  basic 
Open  Hearth  can  handle  with  no  difficulty  what- 
ever, and  to  this  is  to  be  attributed  the  wonderful 
increase  in  recent  years  of  basic  Open  Hearth 
steel  production. 

METHOD 

In  general,  the  principles  and  methods  em- 
ployed in  the  removal  of  carbon  silicon  and  man- 
ganese are  identical  with  those  employed  in 
acid  practice,  it  being  due  only  to  the  addition 
of  lime,  with  the  consequent  forming  of  a  basic 
slag,  that  there  is  any  material  departure  from 
acid  practice. 

The  use  of  this  basic  slag  is  made  possible  by 
the  basic  magnesite  lining  employed,  as  of  course 
an  acid  lining  would  immediately  scour  away. 

75 


A    STUDY    OF    THE    OPEN    HEARTH 

PHOSPHOROUS 

Under  the  oxidizing  influences  of  the  flame 
and  ore,  the  phosphorous  is  oxidized  to  phosphoric 
acid,  2P  +  50  =  P2O5,  which  in  turn,  in  the  pres- 
ence of  lime,  unites  to  form  a  phosphate  of  lime, 
practically  stable  under  normal  basic  Open 
Hearth  conditions,  i.  e. ,  where  the  slag  is  main- 
tained strictly  basic,  but  under  certain  conditions 
a  proportion  of  the  phosphorous  may  easily 
return  to  the  bath  if  propor  precautions  are  not 
observed. 


Sulphur  is  removed  partly  in  the  slag  as  a 
sulphide  of  calcium,  CaS,  by  manganese  ore 
which  may  be  added,  and  by  metallic  manganese 
with  the  formation  of  manganese  sulphide,  MnS. 
Another  method  for  the  removal  of  sulphur  is 
the  so-called  "Saniter"  process,  dependent  upon 
the  use  of  oxychloride  of  lime. 

LIME  ADDITION 

The  lime  may  be  used  in  either  the  natural 
state  of  limestone,  CaCO3  (+  impurities)  or  in  its 
calcined  form,  CaO,  from  which  the  carbonic 
acid  gas  has  been  driven.  On  the  one  hand 
the  use  of  the  limestone  with  its  calcination  in 
the  Open  Hearth  and  consequent  liberation  of 
CO 2,  serves  to  make  the  bath  boil  and  insures  a 
lively  reaction  and  proper  mingling  of  its  ele- 
ments. The  COa  gas  also  acts  as  an  oxidi- 
zing agent,  under  these  conditions  allowing  a 

76 


A    STUDY    OF    THE    OPEN    HEARTH 

larger  quantity  of  pig  to  be  used  with  a  corre- 
spondingly larger  amount  of  metalloids  to  be 
oxidized. 

This  involves  the  following  reactions: 

Carbon :     C  +  CO2=  2  CO. 
Silicon:     Si  +  2  COa=  2  CO  +  SiO8. 
Manganese :     Mn  +  CO*=  CO  +  MnO. 

On  the  other  hand,  the  decomposition  of  CaCOs 
into  CaO  +  CO2  is  one  requiring  the  expenditure 
of  heat  which  must  come  from  the  furnace  and 
consequently  retards  its  working  to  an  appreci- 
able extent.  There  is  also  undoubtedly  more 
tendency  to  boiling  or  frothing  of  the  slag  and 
metal  as  the  gases  escape,  and  more  care  is  nec- 
essary as  to  the  amount  of  ore  added  that  the 
boiling  may  not  become  too  violent. 

Although  Campbell  advocates  a  preliminary 
roasting  which  would  decrease  greatly  the 
amount  of  lime  necessary  to  charge  (also  neces- 
sitating more  ore),  it  is  by  far  the  more  general 
practice  to  use  raw  limestone.  The  fact  that 
more  ore  is  required  as  an  oxidizing  agent  when 
the  limestone  is  calcined  before  use,  is  in  no  way 
an  argument  against  such  preliminary  roasting, 
however,  as  practically  all  the  iron  of  the  ore  is 
reduced  and  absorbed  by  the  bath  as  metal. 

Although  both  the  iron  ore  and  the  lime,  each 
acting  as  oxidizing  agents,  are  in  a  measure 
interchangeable,  the  lime  must  be  in  such  pro- 
portions as  to  keep  the  slag  distinctly  basic  to 
supply  a  base  with  which  phosphorous  can 


A    STUDY    OF    THE    OPEN    HEARTH 

combine  to  form  a  stable  compound.  The 
phosphorous  can  of  course  unite  with  the  iron 
oxide  as  well  as  with  the  calcium  oxide,  but  with 
the  former  the  iron  will  again  be  reduced  and 
the  phosphorous  return  to  the  bath. 

ORE  ADDITIONS 

The  ore  performing  in  the  basic  process  the 
same  functions  as  in  the  acid,  one  of  oxidizing, 
there  is  yet  this  difference,  i.  e.,  it  may  be  added 
at  the  beginning  of  the  operation,  as  with  a  basic 
bottom  there  is  no  danger  of  its  attacking  this  as 
in  the  acid,  where  the  ore  is  usually  added  only 
after  the  heat  is  melted  and  the  bottom  protected 
by  the  bath  charged  with  impurities.  Conse- 
quently the  work  may  be  much  hastened  in  basic 
practice. 

CHARGE 

The  same  general  principles  covering  the 
proportions  of  pig  and  scrap  govern  here  as  in 
acid  practice,  the  exact  proportions  depending 
on  the  cost,  quantities  available  and  the  relative 
analyses  of  the  pig  and  scrap.  However,  a  much 
larger  proportion  of  pig  can  be  used,  as  there  are 
more  oxidizing  agents  at  work  and  for  a  longer 
period.  Furthermore  the  charge  may  in  basic 
practice  be  wholly  of  molten  pig  or  "hot  metal," 
as  the  bottom  protected  by  the  layer  of  limestone 
if  not  subject  to  scorification  as  is  the  acid 
bottom  if  hot  metal  is  poured  upon  it. 

The  pig  must  be  comparatively  low  in  silicon, 
not  over  say  i  per  cent,  as  with  more  than  this 

78 


A    STUDY    OF    THE    OPEN    HEARTH 

.  the  slag  is  so  heavy  as  to  make  trouble,  too  large 
a  quantity  of  lime  being  necessary  to  combine 
with  the  silica. 

Phosphorous  is  so  far  under  control  that  from 
90  per  cent,  to  practically  all  of  it  can  be  removed 
in  the  slag,  so  that  stringent  specifications  in 
regard  to  this  element  in  the  pig  analysis  are 
unnecessary. 

Both  pig  and  scrap  should  be  as  low  as 
possible  in  their  sulphur  content,  inasmuch  as 
this  is  by  far  the  most  difficult  one  of  the  impur- 
ities to  remove  in  a  satisfactory  manner.  The 
sulphur  in  the  pig  should  run  under  .05  per  cent. 

The  limestone  should  have  as  few  impurities 
as  possible  inasmuch  as  its  contents  of  CaO 
(when  calcined)  is  the  measure  of  the  work  it 
will  perform,  and  it  is  evident  that  whatever 
proportion  of  silica  may  be  in  the  limestone  must 
first  be  satisfied  by  its  own  CaO  before  the 
balance  of  the  oxide  is  available  to  perform  its 
work  in  oxidization. 

As  regards  the  ore,  it  is  identical  with  that 
already  covered  under  acid  practice. 

Following  is  a  typical  n6,ooo-pound  charge 
for  5o-ton  basic  Open  Hearth  working  an  axle 
steel  heat : 

Molten  and  cast  iron, 

55, 700  pounds  =  48      percent. 
Steel  scrap,  59,620  pounds  =  51.5  per  cent. 

Additions: 

Ore,  2,000  pounds  =     1.7  per  cent. 

Ore  (fed)  3,000  pounds        =     2.5  per  cent. 


A    STUDY    OF    THE    OPEN    HEARTH 

Feldspar,  250  pounds      =  .  i  per  cent. 

Lime,  6,800  pounds         =  5.8  per  cent. 
Calcined  dolomite,  1,800 

pounds                        =  1.4  per  cent. 

Rods,  130  pounds             =  .1  per  cent. 

Additions  in  ladle: 

Coal,  281  pounds. 
Ferro,  500  pounds. 

METHOD  OF  CHARGING 

There  is  considerable  variation  in  the  matter 
of  charging,  the  more  common  method,  however, 
being  to  first  charge  all  or  practically  all  of 
the  limestone,  then  the  pig  iron  and  lastly  the 
scrap.  This  may,  however,  be  varied  by  charg- 
ing only  a  small  portion  of  the  limestone  first 
and  adding  more  from  time  to  time  to  keep  the 
slag  strictly  basic.  The  order  of  charging  the 
pig  and  scrap  may  also  be  reversed. 

A  portion  of  the  ore  is  also  usually  charged 
with  the  limestone  and  scrap,  as  the  heat  then  has 
the  benefit  of  its  oxidizing  action  during  the  full 
period  in  which  the  metal  is  in  the  furnace,  but 
it  is  also  sometimes  introduced  only  after  the 
heat  is  melted,  as  in  acid  practice. 

ELIMINATION  OF  PHOSPHOROUS 

The  exact  period  at  which  the  phosphorous  is 
eliminated  is  very  difficult  to  determine,  and  is, 
furthermore,  dependent  in  a  great  measure  on 
the  particular  practice  followed.  The  following 
table  from  Campbell  shows  the  elimination  after 
melting  in  this  particular  series: 


A    STUDY    OF    THE    OPEN    HEARTH 


iff& 

r 


O 

£ 


00         O         M         « 


oo 


u->       co        o 

in        o       C?> 


5  a 


00 

Q\          O\ 


s  5 


W      <T>     M      M 
O  '    M      O*      O 


§.s  ° 


a      a      n      c 
o      o      o      o 


Si 


A    STUDY    OF    THE    OPEN    HEARTH 

With  low  phosphorous  it  may  be  practically 
all  eliminated  during  melting,  but  this  does  not 
hold  good  with  a  high  phosphorous  charge.  It 
is  important  that  this  element  should  be  removed 
before  the  carbon  is  down,  as,  with  the  carbon 
practically  all  oxidized,  there  is  great  difficulty  in 
removing  the  last  traces  of  phosphorous.  In 
such  a  case  it  may  be  necessary  to  pig-back  and 
again  get  the  metal  on  the  boil,  adding  fresh 
quantities  of  limestone  to  the  charge. 

The  slag  must,  moreover,  be  kept  highly 
basic  with  limestone,  so  that  there  may  be  ample 
lime  with  which  the  phosphoric  acid  may  unite. 
If  at  any  time  the  slag  becomes  too  weak  in  this 
base,  the  phosphorous  tends  to  return  to  the 
bath.  The  slag  may  have  insufficient  lime,  in 
spite  of  the  fact  that  ample  quantity  has  been 
charged,  due  to  the  fact  that  it  tends  to  become 
somewhat  viscid  under  the  heat  and  stick  on  the 
bottom.  By  the  time  the  heat  is  melted  the  bot- 
tom must  be  thoroughly  rabbled  to  make  sure 
that  all  the  lime  is  up ;  this  not  only  on  account  of 
its  necessary  presence  for  the  chemical  reaction, 
but  otherwise  the  bottom  will  so  build  up  as  to 
greatly  reduce  the  capacity  of  the  furnace. 

A  sample  is  taken  after  the  charge  is  melted, 
and  on  quenching  the  fracture  will  show  whether 
the  elimination  of  the  phosphorous,  as  well  as 
the  carbon,  is  proceeding  satisfactorily.  Too 
high  phosphorous  will  show  in  the  fracture  in  a 
crystalline  form  termed  "phosphorous  cross." 
With  the  usual  stock,  however,  and  of  fairly 

82 


A    STUDY    OF    THE    OPEN    HEARTH 

low  phosphorous  metal,  this  element  will  be 
eliminated  by  the  time  the  carbon  is  sufficiently 
oxidized. 

ELIMINATION    OF    SULPHUR 

No  element  is  so  irregular  in  its  elimination 
as  sulphur,  the  practice  in  some  mills  being  to 
allow  no  higher  average  percentage  in  the  stock 
than  is  allowable  in  the  ingot.  Others,  however, 
regularly  remove  from  20  to  30  per  cent.,  while 
by  the  employment  of  special  processes  as  high 
as  50  to  75  per  cent,  may  be  eliminated. 

With  metallic  manganese  the  sulphur  forms  a 
sulphide,  MnS,  which  tends  to  separate  from  the 
bath,  a  portion  being  absorbed  by  the  slag  and  a 
part  may  be  decomposed  by  the  heat,  the  sulphur 
burning  and  the  manganese  returning  to  the 
bath.  Manganese  ore,  preferably  added  to  the 
charge,  is  reduced  to  metallic  manganese,  its 
action  in  the  removal  of  sulphur  being  as  already 
indicated.  The  following  reactions  are  involved : 

Mn+FeS=MnS+Fe 
MnS+2O=SO2  +  Mn 

As  indicated,  the  portion  of  sulphur  removed 
in  the  slag  is  as  a  sulphide.  The  amount  is 
greatly  dependent  on  the  excess  of  lime  as  well 
as  the  temperature,  a  hot  working  furnace  and 
fluid  slag  being  always  an  aid.  If  the  furnace 
works  sluggishly,  the  elimination  is  not  only 
less  in  quantity  but  more  erratic.  It  involves 
the  following  reactions: 

S  +  CaO  +  C  =  CaS  +  CO 
MnS  +  CaO=  CaS+MnO 

83 


A   STUDY   OF   THE    OPEN    HEARTH 

With  the  use  of  the  "Saniter"  process,  i.  e., 
oxychloride  of  lime,  an  exceedingly  basic  slag  is 
carried  previous  to  the  introduction  of  the  oxy- 
chloride, in  fact,  so  basic  as  to  have  50  to  60  per 
cent,  of  lime,  and  it  is  Campbell's  suggestion 
that  this  excess  basicity,  together  with  the 
marked  fluidity  due  to  the  oxychloride  of  lime, 
enables  the  slag  to  absorb  the  greater  amount 
of  sulphur. 

As  a  whole,  quantitative  determinations  of 
sulphur  are  throughout  very  difficult  to  make 
and  sometimes  misleading.  Not  only  is  it  diffi- 
cult to  determine  the  exact  proportions  of  sul- 
phur in  the  charge,  it  requiring  very  complete 
and  laborious  sampling  to  get  this  accurately, 
but  with  producer  gas  and  the  use  of  a  compar- 
atively high  sulphur  coal,  the  absorption  from 
this  source  introduces  sulphur  in  unknown  and 
sometimes  excessive  quantities. 

SLAG 

In  the  basic  process  the  slag  requires  proba- 
bly somewhat  more  careful  watching  than  in 
acid.  Not  only  is  its  volume  much  greater,  but, 
contrary  to  acid  practice,  one  of  its  impurities 
already  oxidized  may,  unless  the  slag  has  proper 
attention,  return  to  the  bath. 

Its  composition  includes  of  course  the  silica 
from  the  oxidization  of  the  silica  in  the  pig  iron, 
and  any  present,  as  impurities,  in  the  limestone, 
ore,  etc. ,  oxides  of  calcium,  iron  and  manganese, 

84 


A    STUDY    OF   THE    OPEN    HEARTH 

the  latter  from  the  pig  and  also  from  the  man- 
ganese ore  sometimes  added;  also  alumina  from 
the  impurities  in  the  lime,  ore,  dolomite,  etc.,  as 
well  as  magnesia  taken  up  from  the  bottom, 
together  with  whatever  phosphorous  may  have 
been  oxidized  and  held,  as  phosphoric  acid,  and 
subsequently  as  phosphate  of  lime,  together  with 
a  variable  amount  of  sulphur  in  the  form  of  cal- 
cium sulphide. 

The  two  primary  essentials  in  basic  slags  are 
basicity  and  fluidity.  On  the  basicity  depends 
its  power  to  hold  and  take  up  sulphur  and  phos- 
phorous, and  unless  sufficiently  basic  it  will  also 
rapidly  cut  away  the  bottom.  It  must  be  fluid 
in  order  to  properly  work  the  heat,  pour  cleanly 
from  the  bottom,  in  order  that  the  latter  may  not 
fill  up,  and  last,  but  by  no  means  least,  on  its 
fluidity  as  well  as  its  basicity  depends  in  a  very 
great  measure  its  ability  to  remove  the  phos- 
phorous and  sulphur.  Such  oxides  of  iron  and 
manganese  as  are  present  tend  to  render  the  slag 
more  fluid,  while  the  magnesia  increases  its  vis- 
cosity. If  too  thick,  the  slag  may  be  thinned  by 
the  addition  of  a  little  calcium  fluorspar,  calcium 
fluoride,  CaF2.  This  increases  the  fluidity  with- 
out lowering  its  basicity.  Manganese  ore  is  also 
sometimes  used  with  the  additional  advantage 
that  it  is  a  de-sulphurizing  agent.  Silica  in  the 
form  of  brickbats,  often  employed  for  this  pur- 
pose in  acid  practice,  would  be  here  entirely 
unsuitable,  as  the  slag,  though  rendered  more 
fluid,  would  be  also  less  basic,  and  not  only 

85 


A    STUDY    OF    THE    OPEN    HEARTH 

retard  the  de-phosphorization,  but  allow  a  portion 
of  the  phosphorous  already  oxidized  to  return  to 
the  metal.  Such  a  slag  would  also  rapidly  erode 
the  bottom  and  walls  at  the  slag  line. 

Some  explanation  is  due  for  the  presence  of 
oxide  of  iron  in  the  slag,  as  there  is  an  excess  of 
calcium  oxide  to  satisfy  the  silica.  The  idea 
advanced  by  Campbell  is  that  slags  tend  to  com- 
bine with  whatever  will  promote  their  fluidity. 
A  slag  made  up  almost  wholly  of  silicate  of  lime 
is  very  viscous,  consequently  seizes  upon  the 
iron  as  conferring  fluidity.  Without  going  into 
detail  his  conclusion  is  that  the  regulation  of  the 
percentage  of  SiO3  +  FeO  in  the  slag  is  practi- 
cally automatic. 

The  following  analyses  show  typical  basic 
slags  from  normal  axle  steel  heats,  the  charge 
being  made  up  of  47  per  cent,  molten,  or  cast 
iron,  and  51  per  cent,  steel  scrap. 

SiO8  FeO  P8O5 


11.50    '     .          .         16.66  .  .  2.97 

12.40         .          .         18.39  •  •  z-68 

13.70         .          .         17.78  .  .  2.35 

16.20         .          .         14.73  •  •  2-°7 

13.20         .          .         15.24  .  .  2.85 

14.10     .    .          .         21.34  .  .  2.67 

23.40         .          .         11.68  .  .  3.48 

and  the  more  complete  analysis  of  slag  ready  to 
tap,  showing: 

86 


A    STUDY    OF    THE    OPEN    HEARTH 

SiO2  .  .  10.80  per  cent. 

FeO  .  .  .  22.01   per  cent. 

AUOs  .  .  .  1.55  per  cent. 

P2O5  .  .  •  5.61  per  cent. 

MnO  .  .  .  9.00  per  cent. 

CaO  .  .  .  44.00  per  cent. 

Mgo  .  .  .  6.53  per  cent. 

REMOVAL    OF    SLAG 

When  the  ore  is  charged  with  the  stock,  there 
is  of  course  a  very  considerable  oxidizing  action, 
the  slag-  in  the  earlier  stages  containing  often 
large  percentages  of  phosphoric  acid.  Both  on 
account  of  the  large  volume  of  slag,  the  use 
of  both  ore  and  limestone  tending  to  make  it 
foam,  and  the  liability  of  the  phosphoric  acid 
once  in  the  slag  returning  to  the  metal,  removal 
of  the  slag,  partial  or  entire,  has  often  been  sug- 
gested. In  an  ordinary  furnace,  however,  this  is 
difficult  to  do  without  wasting  metal,  as  the  slag 
line  is  often  very  variable,  and  if  tapped  low 
enough  to  get  all,  a  small  portion  of  the  metal  is 
often  brought  with  it.  It  is,  nevertheless,  regu- 
larly done  at  some  plants,  particularly  where 
rolling  or  tilting  furnaces  are  used. 

RECARBURIZATION 

This  is  practically  identical  with  recarburiza- 
tion  in  acid  practice.  It  is  very  common,  how- 
ever, in  basic  practice  to  have  in  the  decarburized 
metal  considerable  content  of  manganese  either 
from  manganese  ore  introduced  to  promote  fluid- 
ity and  the  removal  of  sulphur,  or  from  the  stock, 

s? 


A        STUDY        OF        THE         OPEN         HEARTH 

and  due  account  must  be  taken  in  the  ferro  addi- 
tion. Furthermore,  any  carbon  added  must  be 
made  in  the  ladle,  as,  if  the  heat  is  recarburized 
in  the  furnace  in  contact  with  the  slag,  a  portion 
of  the  phosphorus  may  return  to  the  bath. 


A    STUDY    OF   THE    OPEN    HEARTH 

CHAPTER   VI 

SPECIAL    PROCESSES 
TALBOT    PROCESS 

What  is  often  termed  the  Continuous  Open 
Hearth  process  was  patented  by  Talbot,  of 
Pencoyd,  in  1899.  In  this  process  a  modified 
tilting  or  rolling  open  hearth  of  large  capacity  is 
used,  often  holding  200  tons  or  over. 

The  initial  charge  of  scrap  and  pig  is  worked 
in  the  usual  manner,  but  when  ready  to  tap,  say 
only  25  to  30  per  cent,  of  the  purified  metal  is 
withdrawn. 

To  the  remaining  metal  is  added  oxide  of 
iron  in  the  form  of  roll  scale,  mill  cinder  or  iron 
ore.  After  this  is  melted  and  incorporated  in 
the  .slag,  hot  metal  and  limestone  are  added,  the 
addition  equalling  in  amount  that  already  tapped. 

Due  to  the  slag,  now  very  rich  in  oxides  of 
iron,  the  reactions  are  violent  and  purification  is 
very  quickly  effected,  the  percentage  of  impuri- 
ties in  the  hot  metal  added  being  of ,  course 
much  reduced  by  dilution  with  the  metal  already 
purified  in  the  furnace.  The  above  additions  are 
made  not  at  once,  but  at  intervals,  dependent 
upon  the  particular  practice  and  the  violence  of 
the  reactions.  This  process  is  repeated  as  often 
as  the  metal  is  sufficiently  purified;  at  the  end 
of  the  week,  however,  it  is  usual  to  tap  the  entire 
charge  and  make  necessary  repairs.  The  es- 
sential principle  involved  in  the  exceptionally 
vigorous  reactions  brought  about  upon  the  hot 

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A    STUDY    OF   THE    OPEN    HEARTH 

metal  by  the  slags,  exceptionally  high  in  metallic 
oxides  and  consequently  readily  reducible  by  the 
metalloids  of  the  bath.  This  method  of  opera- 
tion has  the  advantage  of  being  applicable  to 
the  pig  and  ore  process,  of  allowing  considerable 
variation  in  the  analysis  of  the  metal  used,  and 
of  producing  a  large  tonnage.  It  is  particularly 
desirable  where  economy  of  space  is  necessary. 

MONELL    PROCESS 

This  is  essentially  that  of  the  Talbot,  i.  e., 
dependent  upon  the  strong  oxidizing  action  of  a 
slag  rich  in  oxides  of  iron.  It  is  carried  on  in  the 
usual  stationary  furnace,  charging  the  limestone 
and  iron  oxides  first,  heating  them  until  almost 
melted  and  then  adding  the  molten  pig.  After 
purification  the  entire  heat  is  tapped.  In  tap- 
ping the  entire  heat,  the  heavy  and  corrosive  slag 
necessarily  comes  more  in  contact  with  the  fur- 
nace bottom  than  in  the  Talbot  process,  and  con- 
sequently careful  attention  to  bottom  repairs  is 
necessary, 

BERTRAND-THIEL    PROCESS 

This  has  been  developed  abroad  and  is  espe- 
cially adapted  to  high  phosphorous  pig  iron. 
Two  furnaces  of  the  ordinary  type  are  involved. 
Into  the  first  is  charged  molten  pig  or  pig  and 
scrap,  ore  and  limestone,  in  the  usual  manner. 
The  ensuing  reaction  removes  all  the  silicon,  by 
far  the  larger  percentage  of  phosphorous  and  a 
portion  of  the  carbon.  The  metal  is  then  tapped 

90 


A    STUDY    OF    THE    OPEN    HEARTH 

into  the  second  furnace,  in  which  is  an  additional 
charge  of  lime  and  ore,  together  usually  with 
a  certain  amount  of  scrap,  all  heated  to  point  of 
fusion,  and  care  being  taken  that  none  of  the 
slag  from  the  first  furnace  enters.  Here  purifi- 
cation is  completed. 

In  this  process  the  highly  oxidizing  action  of 
a  slag  rich  in  oxides  of  iron  is  again  made  avail- 
able, together  with  the  removal  of  the  first  slag 
holding  the  major  portion  of  the  phosphorous, 
thus  eliminating  any  chance  of  its  return. 

DUPLEX    PROCESS 

This  is  simply  a  combination  of  the  Bessemer 
and  the  Open  Hearth,  and  is  particularly  applic- 
able to  pig  iron  containing  too  high  silicon  for 
advantageous  working  in  either  basic  Bessemer  or 
basic  Open  Hearth. 

In  the  acid  Bessemer  converter  the  prelim- 
inary blast  removes  the  silicon,  together  with  a 
considerable  proportion  of  the  manganese  and  a 
certain  amount  of  the  carbon  The  desiliconized 
metal  is  then  transferred  to  the  basic  Open 
Hearth,  where  the  phosphorous  and  the  remain- 
der of  the  carbon  is  eliminated  in  accordance  with 
the  usual  practice. 

This  process  has  been  employed  in  this  coun- 
try mainly  in  the  South,  where  the  ores  are  such 
as  to  produce  pig  iron  adapted  to  this  treatment. 


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